Access Type

Open Access Dissertation

Date of Award

January 2017

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Civil and Environmental Engineering

First Advisor

JOSEPH E. HUMMER

Abstract

These days, alternative interchanges are attracting the attention of transportation

agencies and designers more than ever. Most of the existing interchanges in the U.S

were built in the 1950s and 1960s when traffic volume was much lower, and the type of

vehicles and driving habits were completely different. Moreover, the knowledge of

highway design and safety is more developed now, and this provides an appropriate

situation to increase the efficiency of interchanges regarding traffic operation and safety

using alternative interchanges.

This research evaluated the performance of two proposed service interchange

designs—the synchronized design which is related to a superstreet intersection and the

Milwaukee B design that is related to a parclo B design--as possible substitutes where

existing interchanges are failing. Over 1700 simulation tests modeled the traffic

operation, pedestrian performance, and safety of six different interchanges (two new

and four existing interchanges) in different conditions of traffic volume, traffic

distribution, left/right turning volume ratios, and heavy vehicle percentage. Then, a cost

estimation and validation procedure were also conducted to complete the analysis.

Overall, the Milwaukee B showed the best traffic operation among all the

interchanges. The synchronized interchange looks promising as a substitute for a

diamond interchange with dominant through traffic. The synchronized and diverging

diamond interchanges (DDI) showed almost the same results while handling moderate

levels of turning volume; however, the synchronized performed better than the DDI in

low turning volumes while the DDI can be a better choice in high turning ratios.

Regarding the safety, the DDI and Milwaukee B were the safest designs based on

observed conflicting interactions in the simulation models; however, the DDI did not

seem as reliable from the viewpoint of unusual maneuvers and wrong way movements.

The new synchronized interchange, the parclo B, and the Milwaukee A (an existing

interchange in Milwaukee, WI) showed the same rate of conflicts. The synchronized

interchange may be advantageous because it was estimated to reduce the severity of

crashes due to fewer crossing conflicts, a lower speed of conflicts, and a higher time to

collision. The results of the pedestrian analysis indicated that a relatively safe condition

is expected for pedestrians in the proposed new designs in comparison to the existing

interchanges. The DDI, one of the most popular alternative interchanges, showed the

worst performance in all the aspects of the pedestrian analysis.

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