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SR = The right-turn saturation flow rate in vehicles per hour. NUMERICAL ILLUSTRATION OF ATL VOLUME PREDICTION A two-CTL approach carries a through traffic flow rate of 1,000 vehicles per hour along with 191 right turns per hour in an exclusive right-turn pocket during the peak 15-minute period. The approach is signal controlled and receives an effective green time of 30 seconds in a 120-second cycle. The traffic engineer is contemplating converting the short right-turn pocket into a shared ATL. The engineer is also interested in testing the effect of adding an exclusive through ATL on the approach. The ATL use and feasibility will be estimated for both scenarios. Shared ATL Scenario Using Equation 3-4 and assuming that the adjusted ST = 1,800 vph per lane and SR = 1,800 x 0.85 = 1,530 vph per lane, then The predicted ATL through flow rate from Equation 3-5 is: The relevant upper-bound value for through traffic in the shared ATL is computed from Equation 3-8, with N = 3 In this scenario, the volume prediction from Equation 3-5 is lower than the volume using the equal v/s criterion. The shared ATL is predicted to attract 157 existing through-movement vehicles per hour, or about 16 percent of the total through-movement flow. The lateral through-lane volume distribution will be 157 + 191 = 348 vph in the shared ATL, and (1,000 -157)/2 = 422 through vehicles per hour in each of the two exclusive CTLs. Page 27

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Exclusive ATL Scenario In this case, Equation 3-4 is used with XR set to 0, yielding VATL = 202 vph, which is higher than the shared lane case, as expected. The maximum value of through traffic that equalizes the queue service time is estimated from Equation 3-7 using a default HCM 2010 value of lane utilization fLU = 0.908 (2, Exhibit 18- 30). Substituting into Equation 3-7 gives VATL, MAX = 265 vph. The estimated exclusive ATL flow rate is the lower of the two estimates at 202 vph, and the per - lane through flow rate in the CTLs is (1,000 202)/2= 399 vph. It is clear from the analysis that either the shared or exclusive ATL scenario will relieve the approach congestion considerably. By comparing the before-and- after v/c ratios, one can see that while right turns may experience a higher v/c ratio and higher delays in the shared lane scenario, through traffic will benefit considerably from the ATL addition. A summary of the computed v/c ratios in the three scenarios is depicted in Exhibit 3-8. Further estimates of delays, LOS, and queue lengths associated with ATL installations are provided with the computational engine described in Appendix B. A first-cut analysis of the example results would indicate that converting an exclusive right-turn pocket to a shared ATL appears to be a sufficient treatment in the short term, assuming current flows and signal plans do not change appreciably, and that the ATL's length is dimensioned properly. Exhibit 3-8 Baseline v/c After Conversion v/c After Adding Movement and Lane v/c Movement v/c to Shared ATL Exclusive ATL* Ratios Before and After ATL Through Traffic 1.167 0.984 (in CTL) 0.50 in ATL Conversion or Addition 0.93 in CTLs Right-Turn Traffic 0.50 0.850 (traffic in shared ATL) 0.50 * Exclusive ATL scenario assumes maintaining the exclusive right turn lane Page 28