This document was a graduate-level academic exercise to learn how to prepare a professional traffic impact analysis for a proposed commercial site plan. The development is fictitious, however this site (zoning, traffic counts, et. al) are based on real world conditions and field observations. This was written to meet the Utah Department of Transportation‘s requirements for access management along University Avenue (US-189).
A new regional shopping center is proposed to be constructed on two vacant parcels of land at approximately 1300 South University Avenue. The new development, called Los Gordos Plaza, will feature three commercial tenants. These include: (1) a Carino’s Italian will occupy 6,522 square feet on a pad facing University Avenue, (2) a tire superstore will occupy 16,000 square feet on a second pad adjacent to University Avenue and will face an internal collector road that will serve as an eastern entry to the shopping center, and (3) a two-story general office building that will offer 36,000 square feet of new space on an 18,000 square foot pad that will face 1200 South. In total, 58,500 square feet of new commercial space will be added onto the 5.86-acre lot with 225 new parking spaces added.
The site will generate new vehicle trips and customers enter and exit the site, as well as drive through adjacent intersections to access the site. To determine what impact these trips will have a traffic impact study area was examined. It encompasses the four streets adjacent to the site and their intersections with one another. Streets include: 1200 South to the north, University Avenue to the east, Towne Centre Drive to the south, and Towne Center Blvd to the east. University Avenue is a high-volume regionally-significant principal arterial street and has two coordinated signalized intersections at 1200 South and Towne Center Drive (East Bay Blvd). Towne Center Blvd. (not to be confused with Towne Center Drive) serves as the mall’s ring road and has one signalized T-intersection at Towne Center Drive and an un-signalized intersection (3-way stop sign) at 1200 South. Driveways to the development will have stop signs for traffic exiting the site but the cross traffic on the street will not have a stop sign.
The development would involve closing three existing driveways on University Avenue, closing an adjacent mini-mall’s driveway to University Avenue, and one of Chevron’s driveways. These would be consolidated into a single new access that aligns with a driveway to Sam’s Club across the street. A driveway to 1200 South would be widened and rebuilt. These two driveways would act as two 36-foot-wide internal circulation roads that would give access to the parking area. They would meet at a T-intersection controlled by stop signs in the middle of the site. Pedestrian crosswalks would give a place for customers to cross safely between the parking area and their cars. A continuous crosswalk would run north and south through the middle of the parking area to give access to the office building. Parking spaces would be 9-foot by 18-foot, which should accommodate even the largest passenger vehicles currently for sale. Aisles between parking would be at least 27 feet wide. Turning corners near aisles would give enough space for a delivery truck (semi-truck) to turn around without having to back up. Two 100-plus foot long delivery truck areas would be provided on the north-south internal collector road, so deliveries will not block customers entering or exiting the development.
The current number of vehicles turning at or driving through each of these intersections was measured during the busiest time of the afternoon when the site’s impact would be most likely to deteriorate traffic flow on these four adjacent streets. The number of cars (traffic turning counts) were added to traffic modeling software called Synchro. Following guidelines from the Highway Capacity Manual, an engineering manual published by the Transportation Research Board, a level of service (LOS) for each intersection was calculated. LOS gives a letter grade, A (good) through F (failure) to determine if the delay a motorist faces at an intersection is acceptable or not. Based on our current analysis westbound traffic at Towne Center Drive (East Bay Blvd) and University Avenue receives an ‘F’ based on existing volume. Traffic volume in the opposite direction receives an ‘E.’ All other intersections provide acceptable delay with a grade ‘D’ or better.
The estimated number of new vehicle trips were estimated. These are customers who will use their car to access the site and will be turning into and out of the development’s driveways and drive through or turn at adjacent intersections. These estimations follow the Trip Generation Manual, an engineering document published by the Institute of Transportation Engineers. The manual assigns an estimated number of trips per 1,000 square feet of a particular type of business (land use). Using the categories of high-turnover restaurant, tire superstore, and general office it was calculated that 68 new vehicle trips will enter the development each hour and 93 new vehicle trips will exit the development each hour. Some of these customers may have been driving along University Avenue already, seen a business within the development, and decide spur-of-the-moment to enter the site. These trips, called pass-by trips, are subtracted from the new trips along their existing route, since they would have already been part of the background traffic (the current number of vehicles driving down the street without the new development). The trips are still counted where vehicles enter and exit driveways to the development, are counted in their need for parking spaces, and counted in places where their route is different than it would have been without the development being present (for instance, they may turn left at an intersection instead of going straight). The Trip Generation Manual offers guidance on what percentage of trips can be counted as pass-by. In accordance with a pre-planning meeting with Provo City and the Utah Department of Transportation (UDOT), no value higher than 25% was used. The direction each new trip takes to enter and exit the site is influenced by the percentage of overall background traffic that enters or exits the study are from the same direction. The new trips are assigned to specific driveways and intersections that made logical sense based on these estimated directional percentages.
Once the background traffic is added to the new trips and the pass-by trips the traffic impact can be recalculated using the Synchro software. The outcome for opening day (2017) and five-years after opening day (2022) were compared with what the existing traffic would look like, at a 2% growth rate per year, without the development. The development appears to have no significant impact on any adjacent intersection that would cause it to have unacceptable delay (LOS F or failure). The existing intersection at University Avenue and Towne Centre Blvd (East Bay Blvd) does reach LOS F, but does that on its own. The new site traffic does no increase the delay in any significant way. The development, therefore, should have no significant impact on the adjacent streets and intersections within the traffic study area. Since the development is accommodated by existing streets and intersections, no specific infrastructure improvements are proposed.
An applicant wishes to develop a 5.86-acre parcel of commercial real estate in the East Bay area of Provo, Utah. The development, called Los Gordos Plaza, consists of three parcels, which include a restaurant, an office building, and a tire superstore. As part of the development, the applicant requests access to two roads, one owned by the City of Provo, the other owned by the Utah Department of Transportation (UDOT). The site will generate new traffic which impact will be determined for mitigation purposes. It will need to be constructed in accordance with access management guidelines for UDOT and Provo City.
This report will examine the existing non-site traffic conditions and the performance of existing roadways and intersections adjacent to the site. An estimation of new trips the site will generate will be calculated using recommended practices from the Institute of Transportation Engineers (ITE). Existing volumes will be used to estimate the directional distribution these trips will take to enter and exit the site. These new trips will be routed and overlaid onto existing roadways and intersections to see if a noticeable deterioration in level of service (LOS) occurs.
Purpose of Study
This study will examine the proposed impact of Los Gordos Plaza on the study area surrounding the development. This will include a look at existing conditions, the scale and type of development and trips the applicant’s proposed development will generate. The estimated trips generated will be distributed to streets in a manner appropriate with real-life conditions to determine any significant negative impact to adjacent streets and intersections that may need mitigation. The report also contains design for internal circulation and driveway access.
UDOT categorizes Traffic Impact Analyses (TIAs) into four study categories depending on a proposed site’s scale and impact on the study area. Los Gordos Plaza will add 36,000 square feet of general office space, a 16,000-square-foot tire superstore, and a 6,500-square-foot Carino’s Italian restaurant. This totals 58,500 square feet of new commercial space.
The department also breaks adjacent highways into access management categories. This site proposes to connect to University Avenue (US-189). UDOT categorizes this segment of the highway as R-PU and has a functional classification of principal arterial. The site also proposes to connect to 1200 South Street, a road owned by the City of Provo, which does not have a UDOT access management category, but has a functional classification of a local road.
Based on requirements in UDOT’s R930-6 document which governs access management along state highways like University Avenue, it appears this development must apply for a Level II study based on the proposed square footage (Table 1).
The applicant proposes to construct 58,500 square feet of new commercial space, which will include a restaurant, tire superstore, and general office space. The site has 5.86-acre site. It is located near a regional mall and is within two miles of a major freeway interchange. The development is located near the freeway in Provo’s East Bay neighborhood near a regional mall. The site is zoned for regional commercial uses. The development would feature three businesses on three pads. Two pads front University Avenue. The third, an office building, would front 1200 South.
The proposed development is located in the East Bay neighborhood of southern Provo, Utah County, Utah (see Figure 1). The site is adjacent to Provo Towne Centre mall. It is the site of a former motel and retail building that have been demolished. The site is just west of a Chevron gas station and a mini-mall on the southwest corner of 1200 South Street and University Avenue (US-189), bounded by Towne Centre Blvd., the mall’s ring road, to the west.
The proposed site would include restaurant, tire store, and general office space. This requires commercial zoning and is in compliance with Provo City’s existing zoning requirements. The specific ITE land use codes for Los Gordos Plaza include the following:
According to Provo City’s official zoning map, the site is currently zoned SC-3, which allows for regional shopping centers. It allows for the highest land-use intensity for regional shopping centers and is designed for areas close to freeways and major arterial streets for easy access . This appears to be compliant with the applicant’s request (see Figure 2).
The applicant proposes to construct 58,500 square feet of new commercial space over three phases on a 5.86-acre site (see Figure 3). The first phase would include approximately 6,550 square feet restaurant space on a pad closest the University Avenue. A tenant, Carino’s Italian, has been secured for this pad. A second pad will offer 36,000 square feet of general office space. A third pad will feature a 16,000 square foot tire superstore.
Study Area Conditions
The site is a 5.86-acre undeveloped site located in Provo’s East Bay commercial district. It is located on a principal arterial street and has nearby freeway access. It is located next to a regional mall and across the street from a big box development. This section includes a look at the boundaries for the study area, including existing street characteristics and conditions, adjacent land uses, and a customer’s ability to access the site.
Study Area and Street Conditions
The site is bounded on three sides by public streets. To the east it is adjacent to University Avenue, a state highway. To the north it is bounded by 1200 South Street. Towne Centre Blvd., and the mall parking lots bound it from the west. And an adjoining property owner, the Little Suites motel, bounds it on the south.
- University Avenue is a regional highway and urban arterial that connects Wasatch and Utah counties. In this area of Provo, the road is just over 100 feet wide, is paved in concrete, has three 12-foot thru lanes in each direction with two 10-foot shoulders, and a center turn lane that permits left turns. The posted speed limit is 35 miles per hour. The road serves as a connector for south county communities and central Provo, BYU, and communities in Wasatch County. It has curb and gutter on both sides of the street. On the east side the sidewalk in set back from the curb. On the west side the sidewalk is immediately adjacent to the curb. There are no plans to move the sidewalk in the applicant’s development plan.
- 1200 South Street is a city-owned road which has a center median restricting left turns, and is paved in asphalt. It has five 12-foot lanes with no shoulders. It has no posted speed limit but appears to function with traffic at 25-30 miles per hour. For the purpose of this traffic impact analysis, it is assumed traffic travels at 25 miles per hour. Curb, gutter, and sidewalk on both the north and south sides of the road. It serves as the northernmost of two main driveways for traffic entering and exiting the adjacent regional mall.
- Town Centre Blvd. serves as the mall’s ring road and urban collector. It is paved in asphalt and has two 11-foot southbound travel lanes and one 11-foot northbound travel lane. It has a two-way turn lane that permits left turns. It has a posted speed limit of 25 miles per hour. This road is at a higher elevation than the other adjacent roads which makes connection to the applicant’s site difficult. The segment nearest the applicant’s site is owned by Brixton Properties, the owner and operator of Provo Towne Centre mall.
- Town Centre Drive does not immediately bound-in the applicant’s site. The road may serve to help circulate traffic in and around the applicant’s site. It is a five-lane road with two 12-foot travel lanes in each direction and a median in the center that restricts left-turn movements. It has no posted speed limit, but its counterpart road to the east is posted at 30 miles per hour. Town Centre Drive serves as the primary and southernmost driveways for traffic entering and exiting the adjacent regional mall from University Avenue and I-15. It’s paved in asphalt and has curb, gutter, and sidewalk on both the north and south sides. It has free-right tapers at its connection with Town Center Blvd
The study area will examine existing and future traffic conditions on the four streets that comprise the boundaries of the block on which the applicant’s site lies (see Figure 4). In addition to driveway traffic, it will include a non-signalized intersection at Town Centre Blvd. and 1200 South Street and three signalized intersections which include:
- 1200 South Street and University Avenue
- Town Centre Drive (East Bay Boulevard) and University Avenue
- Town Centre Drive and Town Centre Boulevard.
Adjacent Land Uses
All adjacent lots also share the same SC-3 regional shopping center zoning which the applicant’s lot is zoned as.
A property at 1206 S University Avenue to the northeast of the site is a Chevron gas station. The lot at 1326 S University Avenue, to the southeast of the applicant’s lot, is a mini mall. The lot immediately to the south at 1380 S University Avenue is a two-story Little Suites motel. To the west is Provo Towne Center mall, a regional indoor shopping center owned by General Growth Properties.
Across University Avenue, to the east, is a big box retail plaza which a Sam’s Club anchors and once had a K-Mart (which has now closed). It also has five medium-sized box retailers, four smaller “mini-mall”-sized retailers, and six pad site retailers. This complex is nearly half-a-mile long and is bounded by East Bay Boulevard to the south and Provo 900 South Street to the north.
The site offers reasonably-good regional accessibility, particularly for regional traffic heading north and sound, with nearby access to Interstate 15 and being located on University Avenue, both of which are north-south facilities. Nearby neighborhoods can use 900 South Street to cross under the freeway and access the site via Freedom Blvd and Towne Centre Blvd. Traffic from eastern parts of Provo can use East Bay Blvd via 1860 South. In the future Lakeview Parkway, a new arterial that will connect I-15 to the Provo Airport, will provide additional accessibility via the University Avenue interchange with the freeway.
Analysis of Existing Conditions
The lot is approximately 5.86 acres. It’s generally flat and level with the existing ground at 1200 South Street, University Avenue, and the adjacent Little Suites motel. The lot still has some remaining hardscape from previous construction on the site, though the building is clear of existing structures. This hardscape would be removed before construction would begin.
This section looks at the current physical conditions of the ground the site is proposed to be constructed on and its adjacent streets. Existing non-site traffic is studied with intersection counts listed. The performance of existing intersections capability to move cars is calculated and level of service (LOS) is determined for each intersection. A comparison of previous crash rates is calculated to determine if the area is more prone for crashes than would be expected.
Physical Characteristics of Proposed Site
The site is bounded by four intersections. Two of these are coordinated-time signals along University Avenue, a seven-lane principal arterial street. The signal at Provo 1200 North Street offers shared left-turn and thru movements for east-west traffic. North and south traffic has a single dedicated left-turn lane with the possibility for a protected turn, though none was observed during weekday PM peak. The signal at Towne Centre Drive offers fully-protected dual-left turns for all four directions. Both intersections offered dedicated right-turn lanes for all directions.
A third intersection, which is also signalized, is located at Towne Centre Blvd and Towne Centre Drive and is actuated an uncoordinated. The fourth intersection is a non-signalized intersection at Provo 1200 South Street and Towne Centre Blvd. It offers a protected dual-left turn for southbound-to-eastbound traffic and for westbound-to-southbound turns. Right turns are channelized onto and off of Towne Centre Drive.
The fourth intersection, at Provo 1200 South Street and Towne Center Blvd., is an all-way stop. Two lanes carry southbound through the intersection. Dedicated left and right turn lanes are available for westbound traffic. Northbound is a through lane and all turning movements are shared. A curb restricts traffic from entering the parking area within 60 feet or more of this intersection, preventing this from turning into a de facto four-way intersection.
Traffic lanes were counted and measured and are 12-feet wide on University Avenue and Towne Centre Drive. Lanes are 11-feet wide on 1200 South and Towne Centre Blvd. Signal timing data was collected from UDOT and the city.
Traffic volumes were collected during the busiest time of the day that also aligns with a time Los Gordos Plaza will be busier. Using AM peak (morning rush hour) is not recommended because the tire superstore will not have opened and the restaurant does not serve breakfast. Afternoon peak is chosen because the tire store is still open for business, the office employees may be leaving work for the day, and the restaurant is beginning its dinner period. Most importantly, PM peak represents the busiest time for the adjacent roadways and were therefore chosen for the study.
Traffic volume is of most concern for north-south movements along University Avenue. Volume counts exceed 1,000 vehicles per hour for traffic moving parallel to the site along this corridor, as high as 1,770 vehicles per hour. Turning counts to and from Provo 1200 South tended to be fewer than 150 vehicles per hour. At Towne Centre Drive, volumes for all legs were substantial. North-south traffic is similar to Provo 1200 South. Turning movements that steered traffic toward I-15 can be substantial, in the neighborhood of 300 vehicles per hour or more (full counts are available in Appendix A).
Volume at the two 3-way intersections on Towne Centre Blvd. is more manageable, due in part to their geometry which only has three legs instead of two, and because they are away from the University Avenue corridor.
Capacity and Level of Service (LOS)
The Transportation Research Board (TRB) has created a measuring classification to determine the level on congestion on a road and its impact on usability. The board calls it Level of Service (LOS) and they publish it in their engineering design manual called the Highway Capacity Manual (HCM). Service is given a letter grade from A to F, not unlike how a teacher would grade a student’s work, with A describing a totally free-flowing road/intersection and F describing a highly congested road/intersection (see Table 2). Calculations are measured using total delay that an average car might see and rated using the following rubric:
Based on TRB’s criteria, the three signalized intersections near the applicant’s proposed development were analyzed using Trafficware’s Synchro 9 software (see Table 3). An advantage of Synchro is its ability to model two cascading intersections where the second intersection does not have random arrival and is dependent on signal progression from an upstream signal. This is opposed to the Highway Capacity Software (HCS) which models each intersection individually and assumes random arrival. Since University Avenue uses coordinated signals to move a large volume of cars, Synchro is recommended for this traffic impact analysis. Based on Synchro and taking into account timed signal progression that exists, LOS is adequate for all intersection movements except for traffic exiting the adjacent regional mall that wishes to cross University Avenue eastbound (see full report in Appendix B).
Transportation Safety Analysis
A half-mile stretch of University Avenue adjacent the Los Gordos Plaza site has seen 81 collisions over three years (which averages 54 collisions per year per mile). Generally, the majority of crashes involve cars colliding at an angle (see Table 4). This may be possibly due to the number of retail driveways. Special care will be taken with the access design of Los Gordons Plaza to ensure safe spacing.
The number of crashes along the half-mile stretch of University Avenue near the proposed site does not exceed the critical crash rates for the area. Intersection crashes were fewer than the critical rate of 2 crashes per million entering vehicles (MEV) per year (Formula 1). Corridor crashes were fewer than the critical rate of 8 crashes per million vehicle-miles travelled (MVMT) per year (see Table 5).
Since the crash rates are lower than the critical crash rates for the region, it does not appear that this area has a serious existing safety problem.
The proposed site will generate impact on the existing built environment. University Avenue is an already busy street and it is important to determine if the traffic that Los Gordos Plaza customers will generate is going to have a detrimental impact on adjacent streets and intersections.
All site traffic generation data is calculated in accordance with procedures in the ITE Trip Generation Handbook and ITE Trip Generation Manual, 9th Edition. The project has three commercial components that act as traffic generators:
- Carino’s Italian restaurant — 6,522 square feet — Land use code 932
- Tire superstore — 16,000 square feet — Land use code 849
- General office space — 36,000 square feet — Land use code 710
To determine the impact of trips, a design hour is first determined. This should be the busiest typical hour of the week that the study area will see. A tire superstore typically doesn’t open early and will see most of its customer base after work. A restaurant is open for lunch and sees its busiest hours around the late afternoon through evening. An office building sees peaks in the morning, noon, and in the late afternoon at the end of the workday. Since all three land uses have busy periods overlapping in the PM peak, that’s the best time period to select. More importantly, it matches observed conditions during turning count data collection for this study (see Appendix C) which show the peak hour for background traffic at the nearby intersections is between 4:45-5:45 P.M. Even though some land uses, such as the restaurant, have peak times that vary from the background traffic, the design hour that will be used for this study will focus on the background traffic as it has the largest impact on adjacent intersections.
With the design hour now selected, a raw number of new trips generated is estimated. The results are displayed in Table 6. The table shows the potential number of trips that could be generated by these new land uses. Values are determined based on the square footage of each land use. It does not yet take into account customers who may make an unplanned visit while driving past the location nor does it take into account existing customers in the shopping center (see Appendix C).
Pass-by is an estimated figure for trip reduction can be made for existing motorists who are making a trip for a different reason near the site and decide to stop by. These are trips that would enter and exit the study area normally, but are diverted into the site. These are not considered new trips, as the motorist was already driving by, and are therefore subtracted from the figure of the total impact Los Gordos Plaza would generate (see Table 7 and Appendix D).
The rate of pass-by reduction for the restaurant is 43%. The rate of pass-by reduction for the tire superstore is 28%. In both cases, Provo City requests that no rate higher than 25% be used – so that rate was used for reduction. There is no pass-by reduction for the office.
Based on estimates given in the ITE Trip Generation Handbook, 9th edition, the estimated number of total trips generated on a given weekday is 1,555 with 712 entering trips and 843 exiting trips (see
Table 8). This reduces to 1,366 total trips after 189 trips are removed due to pass-by reduction.
Multi-use same-visit trips may be present. These are customers who enter the site to access one of the proposed land uses and decide to patronize a second (or third) land use without entering or exiting the site. In theory, there is a risk such a customer could be double counted and a reduction factor should be taken into consideration. Using a method provided in the ITE Trip Generation Handbook, a possible 32% reduction in trips may be possible (see Appendix E and F). However, under present methods, the accuracy of this reduction estimation cannot be assured cannot be assured. The ITE Trip Generation Handbook offers only a limited number of multi-use examples, including office to/from retail, office to/from residential, and retail to/from residential. This data is also based upon a limited number of samples in Florida and may not appropriately reflect the land use behavior at Los Gordos Plaza. For this reason, a conservative estimate will be taken to assume multi-use trip reduction is zero percent.
There is a possibility that the Provo-Orem TRIP infrastructure installation (bus rapid transit), once complete, could reduce automobile trips further. A station will be constructed within 200 feet of Los Gordos Plaza along Towne Centre Blvd. Additionally, some may arrive at the development on foot or by bicycle. While a noticeable reduction in automobile trips may be possible, it is also possible the benefit may be negligible. To avoid the risk than under-constructing for autos and creating traffic problems, this study will conservatively estimate a 100% automobile trip mode split and not ask for further reductions in trip generation figures.
This is an estimation of the general origin direction for motorized customers arriving at the site and their destination direction when they are leaving. It is useful in predicting which roadways and intersections the new traffic will route through and pose an impact on.
To estimate Trip Distribution, there are two prediction methods which are the Gravity Model and the Analogy Method. There methods are compared and determined which directional distribution should be selected.
The Gravity Model is based on the physics principal of force over distance squared, which mirrors a work equation or Gravity Theory. This formula is adapted to estimate the impact this site will have on attracting new trips based on nearby population and travel time distance (Formula 2).
For the proposed site, a database of Traffic Analysis Zones (TAZs) was divided into four regional categories based upon how vehicles may enter the site (see Appendix H). Each TAZ has an estimated travel time to our proposed site and an estimation of the population that live within its boundaries. Using the equation (Formula 2), an Excel database calculated the proportion of estimated trips that could be expected to enter the site from each categorical direction. This calculation was performed for TAZs within a 10 minute distance of the site, again for those within 15 minutes, and finally for those within 20 minutes (see Table 9).
The site will offer a regionally-significant dining experience that is unparalleled along the Wasatch Front which may attract customers from a greater distance. Additionally, the large tire superstore will offer a larger-than-average selection of tires. As tires are an uncommon purchase, it may indicate a willingness for customers to travel up to 20 minutes. Office space can attract commuters who travel great distances. With this reasoning, the 20-minute estimation of the Gravity Model is selected for further consideration.
The analogy method is a way of estimating how many vehicle trips enter the study area from a specific direction. It assumes the trips generated to and from the site will follow a roughly similar directional pattern as the background traffic does. Therefore, it uses background traffic to estimate future directional splits.
To calculate, this method sums the total volume of cars entering and exiting the study area for the proposed site. The numbers of entering and exiting vehicles for each roadway into the study area were calculated. At the first intersection as the road enters the study area, all turning volumes were added together for the leg entering the site. Volumes that turn toward the exiting roadway on the other legs were also added to that sum to create a total volume for that entry/exit point. These volumes were compared with the total sum for all entries and exits to the study area. This results in percentages that estimate the distribution of new trips the site will generate (see Figure 6 Distribution of entry/exit trips and pass-by trip distribution). As both the SW and NW connections form a ring road around the adjacent regional shopping mall (Towne Centre Blvd.), those two connections are summed to create a single percentage (west). For specific calculations, please see Appendix G.
Directional entry and exit volumes are summed for the roadway segment immediately adjacent to the site (in our case, University Avenue between 1200 South and East Bay Blvd). These two directional sums are divided by the total sum of both for a directional percentage. The results from the northwest (NW) and southwest (SW) entry and exit roads into the study area were combined to create a single western value. The results are displayed in Table 10.
Determining Method Used
Both the Gravity Model and the Analogy Method estimate a distribution of the proportion of trips that could be expected to be generated by the development. A comparison of the percentages between the Gravity Model and the Analogy Method is available in Table 11.
While it is difficult to know if the Gravity Model, as presently constructed, over-estimates traffic entering the site from the west and under-estimate traffic entering the site from the south. Volume on University Avenue, which represents north and south traffic, is monumentally higher than those roads entering the study area from the west. It is true that most of that volume is for commuters passing through the study area and not entering the study area for shopping. That said, entries to the adjacent regional mall are multi-lane and signalized with over 800 vehicles entering the mall from University Avenue. That does not come anywhere close to the volume that appears to enter the mall from the west from single-lane non-signalized entries. That leads one to believe the Gravity Model’s specific construction in this case is flawed because it makes assumptions about traffic origins that do not reflect reality.
Additionally, the Analogy Model reflects real turning count volume that has been recently observed near the site. For this reason, as well as those stated previously, this report will proceed using proportional distribution estimates based on the Analogy Model. The final results are displayed in Figure 6.
This section takes into account the estimated observed non-site traffic volumes, projections for opening-day (2017) non-site volumes, and five-year (2022) estimated non-site volumes. Using these estimations, generated trips are routed in a logical and reasonable manner into and out of proposed driveways. These movements are added to existing turning counts at existing intersections and to the future projections of turning counts at adjacent intersections to see if a notable deterioration in intersection performance happens.
Non-Site Traffic Growth Rate
The proposed development, Los Gordos Plaza, is projected to open in 2017. To adequately measure impact, the proposed development will have on surrounding streets and adjacent intersections, a growth projection must be added to existing turning counts to simulate what conditions may be like on opening day and another five years after opening (in 2022). Existing traffic counts and its growth rate can be seen in Table 12 .
The average shows little to no traffic growth over the previous five years. A few factors are in play, including the 2009 market recession which dropped vehicle miles travelled (VMT) nationally from 2008 to 2014 . Some years have shown negative growth while the economic recovery of 2013-2014 showed over 5 percent growth. A reasonable prediction of 2.0 percent will be chosen at the pre-application meeting and is used for analytical purposes of this proposal.
To calculate new traffic volumes that represent 2017 and 2022, respectively, a run-of-the-mill compounding growth formula was used:
The formula was used twice. Once looking one year into the future (n = 1) and again for five years after opening year (n = 6). In both cases the growth rate is 2% (i = 0.02). Vold is set to existing measured turning volumes. The results are displayed in Figure 7 and Figure 8.
The number of new vehicle trips this site generated can be directed in a general direction based on the proportion of inbound and outbound traffic from the Analogy Method mentioned earlier. Applying these percentages to the estimated number of trips results in the overall number of vehicles that should enter and exit the traffic study area to access the development.
Using these numbers, vehicles were manually routed into the site on paper and then routed out of the site. Only valid turning movements were allowed. When multiple choices were presented, a 50-50 split was typically used (when no other ratio is mentioned). See Appendix G for full workout of trips.
Trip assignment is based upon the access plan which calls for two access points (Figure 9), one on the northern end of the site connecting to 1200 South. And second connects to the eastern end of the site onto University Avenue. Seven other accesses would be closed.
- Northern Traffic: These customers enter the site along University Avenue. Since there is no left turn access into the northern driveway from 1200 South (due to a median), all incoming traffic continues straight through that intersection and makes a right turn into the eastern driveway. Exiting traffic is split between the eastern and northern driveways. The eastern driveway vehicles leave the site by turning left onto University Avenue and continuing until they exit the study area. The northern driveways require a right turn onto 1200 South, then a left onto University Avenue.
- Southern Traffic: These customers enter the site along University Avenue, most likely from the I-15 freeway. Turning left onto Towne Centre Drive would require customers to travel 270-degrees around the site to access it. Therefore, all incoming traffic is routed directly to the eastern driveway where vehicles make a left-hand turn into the site. Three-quarters of exiting traffic makes a right-hand turn onto University Avenue from the eastern driveway. One-quarter exists via the northern driveway, right onto 1200 South, and right onto University Avenue.
- Eastern Traffic: These customers enter the site along East Bay Blvd. approaching University Avenue. At the intersection, all traffic makes a right – as continuing straight would require customers to travel 270-degrees around the site. Traffic makes a left into the site from the eastern driveway, as left-turn access is not permitted from 1200 South. Exiting traffic all leaves via the eastern driveway right onto University Avenue and then makes a left to East Bay Blvd.
- Western Traffic: Traffic enters the study area from both sides of the mall on Towne Centre Blvd. Southwestern traffic continues straight through the signal at Towne Center Drive, makes a right turn onto 1200 South, and a right turn into the northern driveway. Northwestern traffic enters from Towne Centre Blvd., makes a left onto 1200 South, and a right into the northern driveway. Exiting traffic all leaves through the eastern driveway, as left turns are not permitted out of the northern driveway. All traffic turns right onto University Avenue and right onto Towne Centre Drive. Southwestern traffic turns left at the signal with Towne Centre Blvd. and exits the study area. Northwestern traffic turns right at the signal, continues straight through the intersection at 1200 South, and exits the study area.
Pass-by Traffic: This traffic represents existing travelers on northbound or southbound University Avenue that enter the site from their respective direction and exit continuing in the same direction. They are split using a percentage based on a ratio of background traffic volume on University Avenue (see Figure 6). Northbound traffic enters the site using the eastern driveway. It exits using a 50-50 split of the northern driveway via 1200 South to University Avenue and directly making a left onto University Avenue from the eastern driveway. Southbound traffic enters the site completely via the eastern driveway. It exits using a 60-40 split of the eastern driveway directly onto University Avenue and via 1200 South right onto University Avenue, respectively (see Figure 10 for diagram).
To calculate total traffic, data were taken from base projections and adjusted for annual growth (see Formula 3). A calculation was made for opening day (2017) and for five years after opening day (2022). These projections only included the base projections and none of the new site traffic. Then new trips were routed through a logical series of turns to represent typical behavior of motorized customers entering the site (see “Traffic Assignment”). These new turning counts were added to the projection values. Finally, pass-by traffic was added to turning counts entering and exiting the site and subtracted from mainline turning counts where the vehicle was no longer present. These three sets of data were combined to create two unified turning count maps which represent all traffic (existing and new) on opening day (2017) and another that represents conditions five-years after opening (2022).
Los Gordos Plaza will be served by two access points. One (eastern driveway) will connect to University Avenue in the center of the development and aligns with the Sam’s Club driveway across the street. By aligning the driveways, it makes the crossing more predictable for motorists and eliminates unnecessary conflict points that are created when driveways are offset. This access will allow left and right turns onto University Avenue and right and left turns from University Avenue. A second access point (northern driveway) will access 1200 South. As this street has a median, only right-in/right-out movements will be permitted.
University Avenue is classified as an “R-PU” street according to UDOT’s access management guidelines. By those standards, set forth in the agency’s R930-6 document, driveway spacing needs to be 350 feet apart. However, this site only has 550 feet of frontage. Even with a proposed closure to the adjacent mini-mall’s driveway (cross access would be provided) only a 577-foot gap remains between existing driveways on neighboring properties. Divided by two, that leaves only 288 feet spacing between driveways. This development will need to request a variance for access. Guidelines for R-U access management (200-foot spacing) can be met.
As an incentive, Los Gordos Plaza is negotiating with two adjacent properties to reduce accesses and use new internal circulation roads as part of this development (Figure 14). Cross access would be given to the adjacent mini-mall at the rear (west) of the existing parking lot and would connect to a new parking area in front of Carino’s Italian (north) in exchange for closing the southern entrance to the mini-mall. This would give the University Avenue (eastern driveway) access 322 feet of downstream spacing. The existing Chevron would keep its southern-most driveway but would close its northern-most driveway and all 1200 South driveways. This clears some conflict out of the intersection functional area at 1200 South (upstream area) and University Avenue (downstream area). In exchange, Chevron would connect to the internal (north-south) collector road and all entry and exit motions would use that driveway. In both cases, driveway volumes were not adjusted as they represent existing trips and not new trips. All existing driveways on the applicant’s site, except for these two new ones requested, will be closed.
In requesting a variance, and in the spirit of good access management principles, the applicant will work to reduce the eight existing driveways (6 of which are on University Avenue) across three sites down to just 3 driveways (2 on University Avenue). While it won’t meet the requested 350-foot spacing, it will increase University Avenue spacing from 119 feet apiece (some are as close as 44 feet) to just two 219-foot and 322-foot spaced driveways (averaging 270 feet, a 27 percent improvement over existing conditions). This demonstrates that even though the access not comply with the provisions of R930-6, it should be allowed as the modifications will improve the operation and safety of the highway compared to present conditions at the site and other non-conforming developments along the corridor.
To construct the new accesses and remove closed accesses, the applicant will apply for an encroachment permit from UDOT, in compliance with R930-6 subsection 8. The contractor will provide flagging operations when required or recommended. While pavement cutting is not anticipated, should it be required it would be acceptable according to R930-6 subsection 5c as the existing concrete pavement is older than 2 years.
To prevent motorized customers from storing their parked vehicles on the street while visiting the site, an adequate number of off-street parking stalls will be provided. The Institute of Transportation Engineers (ITE) offers rough estimates of parking demand in the Parking Generation Manual. Additionally, the City of Provo also offers its minimum parking requirements. In both cases, the number of spaces per land-use intensity (in this case, building square footage) is determined by the type of business. This site includes restaurant, tire store (tire superstore in ITE’s case), and general office land uses (see Appendix K).
Comparing the two sets of requirements, there appears to be a fairly large variation in both the tire store and the office space, while the overall requirements for the restaurant space are identical. The ITE Parking Generation Manual will error on the side of caution and oversupplies parking even for peak hour conditions during the busiest days of the year. It isn’t likely that this development will require the extra 40 spaces beyond what the City of Provo requires. Therefore, the development will exceed the city’s requirement by one space at 225 spaces.
To comply with the Americans with Disabilities Act, the development will provide 7 disabled parking spaces. Guidelines require 7 spaces for parking lots with between 201-300 stalls . That means our 225 general spaces will divide into 218 general-purpose spaces and 7 disabled spaces. One of those spaces will be placed in the prime customer parking area in the eastern Carino’s Italian parking lot. Four more will be adjacent to the pedestrian cross-ways west of the restaurant and tire store. Two more will be available next to the front (southern) entrance of the office building.
This development will provide uniform-sized parking stalls for prime and auxiliary parking spaces. Stall dimensions will be 18 feet long and 9 feet wide. This should accommodate most passenger vehicles and commonly-sized sport-utility vehicles. For instance, one of the largest vehicles for sale in the United States presently is the Lincoln Navigator. Its dimensions are 17.25 feet long and 6.6 feet wide. Every stall in this development will accommodate any vehicle its size or smaller (Figure 15). End aisle islands will typically be about the width and length as the space(s) they abut. Occasionally the islands may be reduced in width, at least partially, to accommodate a turning delivery truck. They will not be reduced in length.
Ninety-degree parking was chosen in lieu of angled parking. This type of parking module design gives customers the flexibility and the best freedom of movement within the development. Angled parking requires one-way traffic down parking aisles. This could be a problem if a delivery truck were to block the end of an aisle, or if a customer were to be slow backing out of a space. Ninety-degree parking allows traffic to enter/exit in either direction down an aisle, preventing unplanned dead ends.
To accommodate 90-degree parking, aisles were spread out across the site to allow generous space for parking and backing out of a space. Most aisles are between 27-to-31 feet wide, which is a generous amount one-and-a-half times longer than even the largest SUVs that may park on the site. The aisle gives two-way traffic nearly 13 feet apiece to pass each other. As this width is wider than a freeway lane, this should help reduce head-on collisions within the parking lot. Granting motorists generous amounts of space, it allows vehicles to safely pass pedestrians who are walking to/from their vehicles in the parking lot. The narrowest aisle is the most southern one which is only 24 feet wide, but does not have any opposing parking spaces.
The site is designed to allow customer vehicles and delivery trucks to access the site free from obstruction. As vehicles leave local streets, they need a road to buffer their speed and allow motorists to psychologically “slow down” to the slow speeds a parking lot requires. In this development, two collector roads serve the eastern and northern access driveways. These roads will have a 20 mile-per-hour speed limit which will prepare motorists for the crawling speeds of the development’s parking lot. The roads will offer three lanes, one in each direction, and a two-way turning lane which can give customers a place to drive around an obstruction when a lane when a lane is impeded. Each lane is 12 feet wide. No parking spaces are directly accessed from the collector roads. Both driveways are 36 feet wide. The northern driveway has a 100-foot throat length which is unobstructed but does parallel a delivery truck storage bay which has a separate lane. The eastern driveway has a 164-foot-long throat for traffic entering the site and a 41-foot-long throat for vehicles exiting the site (Figure 16).
The two internal collector roads meet at a T-intersection in the center of the site. Crosswalks give pedestrianized customers a safe place to access the parking are and cross the collector. This intersection will be stop-controlled to help motorists pay attention to the cross walks, although several other painted pedestrian crossing points exist on the site. The T-intersection will have 45-foot turning radii to accommodate large delivery trucks (WB-62) that may need to access the site  (see Appendix L).
The four northern-most parking modules are designed with end islands shaped to allow a semi-truck to enter from either direction, make a circle around the modules, and exit back out to the internal collector roads. A parking canoe creates the T-intersection and prevents semi-trucks from entering directly into the parking area, getting stuck, and having to back out (see Figure 17 and Appendix L). Two semi-truck parking areas on the north-south internal collector road allow deliveries to be made to the office building and restaurant without blocking the road. A two-way turning lane can also serve as a temporary parking lane for deliveries without blocking internal access. This lane also allows vehicles to turn into and out from parking aisles without impeding internal circulation.
In addition to no parking spaces backing onto an internal collector road, an alleyway gives access to the tire store’s service bays. This prevents vehicles backing out of service bays from interfering with circulation on the internal collector road. This access road has an 18-foot turn around area at its dead end where employees can back a vehicle out of the most inward service bay and drive out of the service area pointed forward. The alleyway is 24-feet-wide which allows vehicles to pass one another without being blocked. The entrance will be marked with “DO NOT ENTER” or “Employees Only” signs to prevent customers from driving in and getting stuck. Tire store employees will drive cars from the customer parking area into the service bays. Signs will be added to the seven northern-most stalls on the canoe, across from the tire superstore, which will indicate those stalls are for “tire store customers only.” This will reduce the probability those spaces will be filled with office employees and reduce the walking distance for tire superstore customers.
Crosswalks throughout the site offer good pedestrian circulation. Pedestrians can access the site from five sidewalks; two along both collector roads, and a sidewalk that runs south of the Carino’s Italian restaurant. Sidewalks have crossing points that allow customers to safely cross the collector roads. The office building’s main (south-facing) entrance aligns with seven parking islands which create a linear pathway for employees to access their vehicles. This pathway also connects to the two primary crosswalks to access the tire store and restaurant.
Traffic and Improvement Analysis
To maintain good traffic flow on streets adjacent to the site, many existing accesses will need to be closed. These include the two Chevron driveways onto 1200 South. This access will be replaced by western cross-access with the development’s new northern driveway. A redundant access for Chevron on University Avenue will be closed and combined with the other existing driveway that is slightly-more downstream. This protects the downstream functional area of the intersection. All existing University Avenue-facing driveways to the applicant’s property will be closed as well as the adjacent mini-mall’s driveway. These will be served by a new internal collector road which will connect to University Avenue at approximately the center of the property, which will split the distance between the signal and the first driveway downstream of the site. Access to the mini-mall will be replaced by cross access from behind the mini-mall site (western) and an extending the mini-mall’s parking lot to connect to the eastern driveway internal collector road (northern). No changes to the adjacent streets are proposed. No signal timing changes are proposed.
Both new driveways will be 36 feet wide with one lane allowing vehicles to enter the site. At the eastern driveway two lanes will be permitted to exit, each 12 feet wide, one allowing left turns and the other right turns. At the northern driveway the left turn lane will be hashed out with painted lines to indicate left turns are not permitted, though the 12 feet will remain to give delivery trucks extra room to enter or exit the driveway.
The throat length for vehicles entering the site will be 100 feet for the northern driveway and 41 feet for right-turning vehicles at the eastern driveway and 95 feet for left-turning vehicles at the eastern driveway. It is easier for a right-turning vehicle to find a gap in the traffic and exit the site. It is assumed the throat storage length is adequate to allow vehicles to leave the site. Left turning vehicles were calculated using Synchro and storage was estimated to be sufficient (Table 14).
Level of Service
Using the Synchro traffic modeling software, the new traffic values for opening year (2017) and five-years after opening day (2022) were entered into the existing model that was used to calculate delay performance for each intersection. This creates a preliminary LOS result which estimates how the adjacent intersections will perform with (2017) and without (2016) development in place. It also takes into account the 2 percent annual increase in background traffic which was already calculated (see Figure 7, Figure 8, and Appendix M).
Nearly all the intersections continue to perform as well or nearly-as-well as before the development was put into place, with a LOS E or better. One of the exceptions is the eastbound through movement on Town Centre Drive. The existing conditions were LOS E nearly pushing the cut-off for LOS F. Since none of our development’s traffic assignments route cars through this motion, it means this movement is failing from the increase in background traffic. The LOS results also display that our proposed development is not responsible for its failure.
Additionally, the exit onto University Avenue for Los Gordos Plaza fails from opening day. This is due to a non-signalized left-turning exit which always requires a long wait for a gap in traffic. While not ideal, it appears to be similar to what one would expect when making a left out of a business.
The motions which the development will be putting new traffic into at 1200 South and University Avenue and at Towne Centre Drive and University Avenue (NB-SB) appear to have little effect on the overall LOS into the future.
The traffic demands of the development appear to be accommodated by the existing infrastructure that is already in place according to LOS analysis. No immediate improvements are recommended.
Future development to the south of Los Gordos Plaza should be encouraged to extend the development’s new north-south internal collector road southward and connect it to Towne Centre Drive with a right-in/right-out connection (Figure 18). This would allow this circulation road to serve as a frontage road behind the businesses that front University Avenue at this development and adjacent properties. This road could replace existing accesses to University Avenue. The new eastern driveway that connects to University Avenue could be adjusted to be right-in/right out which would improve traffic flow as left turns into the site could be served at the Towne Centre Drive signal with traffic proceeding right onto the extended internal circulation road.
The east-west traffic volume at Towne Centre Drive and University Avenue should continue to be monitored. If modeling is correct, these intersection legs are at or approaching unacceptable levels of delay. Although traffic from Los Gordos Plaza does not affect these failing intersection legs, failure at that intersection would have a negative impact on the development and all businesses within the study area. Timing of that intersection should be examined and adjusted appropriately.
Conclusion and Recommendations
The proposed development consists of three new commercial buildings on a vacant 5.85-acre lot on University Avenue adjacent to Provo Towne Centre Mall, which include a restaurant, tire superstore, and a two-story general office building. These land uses are compliant with existing zoning and setbacks meet Provo city requirements.
The traffic study area included the four adjacent intersections to the development of the four adjacent streets, which include University Avenue, Towne Centre Drive, Towne Center Blvd., and 1200 South. The number of vehicle trips during PM peak conditions was counted and a LOS analysis was performed which determined the existing conditions do not result in an unacceptable level of service except for westbound traffic on Towne Center Drive. These traffic volume numbers were grown to reflect conditions when the development opens and five years afterward. While conditions deteriorated slightly, none of the intersections reached unacceptable conditions besides the westbound traffic on Towne Center Blvd. New trips the site will generate were calculated, adjusted for pass-by trips, and then routed in a possible and logical manner onto existing roads and through intersections within the traffic study area. A second LOS analysis was conducted which resulted no deterioration in intersection performance and no unacceptable delay that was not already present within existing conditions. It appears the existing roadway can accommodate the new traffic this development will generate.
The square footage of the three new buildings was used to estimate the new number of parking spaces needed in compliance with city ordinance. It was determined 224 new spaces, 7 of which are disabled spaces, would need to be added. The site plan accommodates 225 parked vehicles, meeting city requirements. The site plan also allows delivery vehicles (semi-trucks) to enter the site, make a full U-turn and exit without backing up or blocking traffic. Two storage areas allow a delivery truck to park without blocking entry and exit to the site.
A safety analysis was conducted and found the stretch of roadway adjacent to the site has a crash rate significantly lower than the critical crash rate. The site does not appear to have any out-of-the-ordinary safety concerns that need to be addressed. Driveway points along University Avenue do not currently meet spacing requirements for the road’s access management classification (R-PU). Six driveways across three properties would close and be replaced by one, with one existing access on an adjacent property remaining open. The new single driveway does not have adequate frontage to meet the spacing requirement – and the developer will request a variance from UDOT to meet access management criteria one level lower (R-U) in exchange for reducing the number of driveways from eight to two. An application for an encroachment permit is necessary to close unused accesses and construct new ones.
As the property adjacent to the development’s southern border is demolished and redeveloped, the applicant strongly suggest the city encourage the new adjacent redevelopment to extend the site’s new north-south collector road all the way to Towne Centre Blvd. This will give rear access to pads that front University Avenue and will allow further reduction of access along University Avenue which will improve traffic flow. The signal at University Avenue and Towne Centre Drive is approaching failure. Although traffic from this development is not a significantly-contributing factor, it is recommend the city explore retiming the signal to improve LOS for the entire study area.
-  City of Provo, “Current Zoning Map,” 12 December 2012. [Online]. Available: http://maps.provo.org/downloads/Current%20Zoning%20Map.pdf. [Accessed 25 January 2016].
-  Transportation Research Board (TRB), in Highway Capacity Manual, 2010.
-  UDOT, “Traffic Maps,” [Online]. Available: http://www.udot.utah.gov/main/f?p=100:pg:0::::V,T:,528. [Accessed February 2016].
-  U.S. Department of Energy, “Annual Vehicle Miles Traveled in the U.S.,” 2015. [Online]. Available: http://www.afdc.energy.gov/data/10315. [Accessed 3 March 2016].
-  City of Provo, “Chapter 14.37: Off-Street Parking Standards,” [Online]. Available: http://www.codepublishing.com/UT/Provo/html/Provo14/Provo143700.html.
-  “Accessible Parking,” [Online]. Available: https://adata.org/factsheet/parking. [Accessed 2016].
-  AASHTO, “Minimun Turning Path for Interstate Semitrailer (WB-62),” in A Policy on Geometric Design of Highways and Streets, 2011, pp. 2-23.
-  Utah Department of Administrative Services, “Rule R930-6 Access Management,” 1 November 2015. [Online]. Available: http://www.rules.utah.gov/publicat/code/r930/r930-006.htm. [Accessed 25 January 2016].
- Appendix A: Intersection turning counts
- Appendix B: Existing conditions Synchro intersection level-of-service (LOS) analysis
- Appendix C: Trip Generation Rates (ITE Trip Generation Manual)
- Appendix D: Pass-by Rates (ITE Trip Generation Handbook)
- Appendix E: Internal Capture Rates (ITE Trip Generation Handbook)
- Appendix F: Workout for internal capture rates within the proposed development
- Appendix G: Workout for trip distribution using Analogy Method
- Appendix H: Workout for trip distribution using Gravity Model
- Appendix J: New trips and pass-by trips workout sheets
- Appendix K: Parking generation rates by land-use type (ITE)
- Appendix L: Geometric design vehicle for internal circulation collector roads
- Appendix M: Synchro intersection LOS analysis data sheets