Project Report

At 16th and Waldo Rd. intersection, NBL and EBR future traffic have considerably increased compared to their existing traffic. This has caused the EBR queue storage ratio to go way over one and the LOS to plunge to E. The LOS of NBL also have deteriorated into C (compared to B during existing conditions). Other movement delays have also increased though their LOS have not fallen below what they were in existing conditions. Furthermore, the approach delays of NB and EB have noticeably increased resulting in the NB and EB LOS’s dropping to E and C, respectively. Queue storage ratios of EBR and WBL have exceeded 1, which are needed to be fixed during mitigation process. At 8th intersection, the approach delays have slightly changed with none of the movement LOS’s falling below D. Also, all the queue storage ratios are less than one.

The internal link leading to Walmart was designed in three different ways in order to determine the most efficient design. In the two-way stop controlled scenario, the eastbound functions very well using one shared lane with an LOS of A. No results are reported for westbound since it has right of way over all other movements thus experiencing literally no delay. Setting the internal link as all-way stop controlled, EBL will not have an LOS better than E even with designing an exclusive left turn lane. The other two approaches can be designed as shared lane since in this way the intersection LOS will be maintained at D. Designing roundabout, all the approaches can be single lane since none of the approach LOS’s will be worse than B. Therefore, roundabout is the best option since it minimizes the intersection delay and number of required lanes on each approach, thus it is the most cost effective option among all design scenarios.

Having described the problems caused by future traffic in the first paragraph, here a number of mitigation solutions will be proposed and discussed. The main goal was to solve the issues as cost effectively as possible. Probably, the most effective mitigation solution is to decrease the cycle length. Long cycle lengths will cause long delays especially when the volume to capacity ratio is far less than one. Below is computed the capacity for cycle lengths of 120 and 90 seconds. Calculations bellow show that when a 120-second cycle length is used, volume to capacity ratio is 0.86 and 0.74 for 8th and 16th, respectively. Volumes are calculated based on taking the critical volume in each phase.

c=1750−1750∗LC

Where: C=cycle length , L=lost time ,c=capacity

C=120 sec , L=20 sec(4 phases )→c=1750−1750∗20120

=1458 vphpl

volume={@8 th, 10252 +204+147+219=1082 vphpl→ vc=10821458

=0.74

@16 th , 11992

+344+315=1258 vphpl→ vc=12581458

=0.86

As shown above, since volume to capacity ratio at neither intersection is close to one, long cycle length would lead to ineffective green times. Therefore, a 90-sec cycle length was used yielding a v/c ratio of 0.91 at 16th using the above computation.

At 8th intersection, yellow and all red indications appear 4 times after applying the mitigation condition which results in less loss in capacity compared to existing conditions where they appear 5 times. In fact, the all-red and yellow clearance time between the 5th and the 6th phase was eliminated (see 8th intersection future condition report sheet).This was achieved through tweaking the phase splits. At this intersection the LOS of EB has improved to C (from D in existing condition), and the LOS’s of the other approaches have been maintained at the same level as they were in existing conditions.

At 16th intersection, SBL used to be protected-permitted. Through mitigation process, the protected phase for this movement was eliminated since the demand was too low (9 vph), which can be accommodated in a permissive-only manner. Before mitigation, the queues of EBR and WBL spilled over to the adjacent through lane, both of which were modified by tweaking the phases and splits together with lengthening the right turn bay of eastbound. The queue storage ratio of EBR was way more than 1 (3.08), thus this movement was added to the 5 th phase of NEMA diagram (happening at the same time as NBL). This together with a more phase split assigned to NEMA’s 5th phase and increasing the turn bay length from 100 to 150 feet, caused the queue storage ratio to fall below 1. WBL queue storage ratio was also slightly more than 1 which was mitigated by giving more split to the corresponding phase (NEMA’s 8 th phase). Having made these changes, the LOS of eastbound and westbound approaches was promoted

from D to C, yet the LOS of the other two approaches were preserved at the same level as those in existing conditions.

At 12th intersection WBR movement was added to the NEMA’s first phase allowing for it to happen at the same time as SBL. Also more split was allocated to this phase leading to SBL LOS promoting to B as well as reduction in the queue storage ratio of WBR. The storage length of WB link was also increased from 75 feet to 150 feet. In fact, it can be set as long as desired unless it interrupts the upstream intersection (i.e. internal intersection), which is about 1000 feet away, and in turn, a 150-feet storage length for this link does not seem to be problematic. Having applied the described changes, all the delays decreased, especially WBR in which the LOS promoted from E to C. Finally, time-space diagram was tweaked manually to maximize “attainability” and “efficiency” although its impact on results was not so significant.