Publication Date



Open access

Degree Type


Degree Name

Doctor of Philosophy (PHD)


Civil, Architectural and Environmental Engineering (Engineering)

Date of Defense


First Committee Member

Chang-Jen Lan

Second Committee Member

Shihab Asfour

Third Committee Member

Wimal Suaris

Fourth Committee Member

Charles Nunoo


This research has three parts. Part 1: The Policy on Geometric Design of Highways and Street provides 5 methods of superelevation (e) distribution. Many states use methods 2 and 5 for low speed, urban and rural high-speed facilities. Method 5 aims to address speed variations; but is complicated, computationally intractable and may violate design consistency. Design recommendation by NCHRP439 accounts for speed variation, tractable; but is cumbersome along with irregular/step-wise design curves. New reliability based e distribution method is developed that addresses the speed variation; which is simple in determining and evaluating acceptable required e rates. At 95% level of reliability, the e rate obtained is lower than that from current practice resulting in cost savings. Part 2: Current practice/research does not address safety issue of the left-turn-bay at high degree of saturation (x). Left-Turn-Bay distance has three components: clearance, breaking to a stop and queue. The variation in the queue length reduces clearance and breaking distance resulting in unsafe breaking. Failure = clearance plus breaking distance < demand. The reliability of the left-turn-bay defined as the availability of the three components for left-turning vehicles to complete clearance and breaking maneuver safely; measured as increase in the deceleration rate over limit of 11.2ft/s2, safety index and probability of failure. Results show that at 95% reliability, current design practice fails when x exceeds 50%. Part 3: Current practice uses mean traffic volumes (Vd) as input for traffic signal control at roadway intersections. Variations in traffic flows affect the performance of intersection measured by the delay per vehicle traversing the intersection in seconds. Peak hour factor (PHF), the hourly volume divided by the peak 15-min flow rate within the peak hour is adopted by Highway Capacity Manual (HCM) to control surge. HCM suggests PHF design value of 0.92 for urban and 0.88 for rural areas. Fixed PHF may lead to increase in delay. Effects of variation of peak hour volumes on intersection signal delays are examined with large data. A new model is developed for PHF and Vd and used in signal timing to minimize intersection delay. The results show that the assumption of Poisson distribution for Vd is not reliable; delay reduction of 6.2 seconds per vehicle is achieved. Annual savings in travel time, fuel consumption and emissions cost is estimated in billions of dollars.


Time Gap; Stochastic; Friction Factor; Environmental Impacts