Graduation Year

2019

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Civil and Environmental Engineering

Major Professor

Qing Lu, Ph.D.

Committee Member

Manjriker Gunaratne, Ph.D.

Committee Member

Gangaram Ladde, Ph.D.

Committee Member

Mingyang Li, Ph.D.

Committee Member

Fred Mannering, Ph.D.

Keywords

Future Highway Cost, Highway Policy, Life Cycle Cost, Managed Lane, Pavement Design

Abstract

Trucks carry major bulk of freight in the U.S. and are likely to continue doing so in the near future for various reasons. They have tremendous impact on highway pavement design and on the costs of pavement construction, maintenance, and rehabilitation. Current policy of truck lane restriction ensures that they mostly use the outside lane(s) on multilane highways. This practice has considerable impact on the cost of pavement construction and rehabilitation. Right now, all the highway lanes are designed and constructed according to the truck load on the outside lane even though the inside lanes receive significantly smaller quantity of load from truck movement compared to the outside lane. The overall construction and rehabilitation cost of highway is clearly influenced by this design uniformity of highway lanes. Comparison of this practice with a group of alternative policy options for flexible pavement shows that the current policy costs much more for the construction of flexible pavement. It is possible to reduce highway pavement life cycle cost by distributing the trucks across the available lanes. But further cost reduction can be achieved by designing and constructing each lane according to the quantity of truck traffic it receives, not the quantity of truck traffic on the outside lane (design lane). Comparable cost reduction can also be achieved by separating truck lanes from the lanes for passenger cars.

Future highway lane management policy will potentially be different from the existing to exploit the benefits of truck platooning to the fullest possible extent. Current literature and results from testing at different parts of the world suggest that the vehicles of future highway system are likely to be connected and autonomous and would be able to form platoons to reduce fuel consumption cost and enhance safety. Within the existing highway lane management policy only limited quantity of truck platooning can be achieved. The possible lane management policy approaches that can allow high degree of truck platooning for connected and autonomous vehicles are assessed for construction, rehabilitation, and fuel consumption cost. One of the possible policy approaches to promote truck platooning is to lift truck lane restriction in the future and direct the truck platoons to use one of the inside lanes of multilane highway segments. If there is higher demand for truck platooning, not achievable with one lane, more lanes can be made available for truck platoons. Opening all the available lanes with high demand for truck platoons can also allow the trucks to assess the possible gaps for the platoon at a certain time and then choose the most suitable lane. In the opposite realm of choices is the conservative approach of allowing some quantity of truck platooning on the outside lane when there is available space headway for the platoons to operate without hampering the movement of entering and exiting vehicles on the outside lane. Choice of lane management policy to promote truck platooning movement can produce very different platoon formation from a range of most basic platooning with two vehicles to full scale platoons with many trucks moving together like a road train. This possible range of platoon formation has an associated range of costs for fuel consumption. Also the flexible pavement construction and rehabilitation cost changes depending on how the platoons are being operated with the choice of lane management policy approach. Assessment of future highway cost elements shows that promotion of truck platooning can reduce the flexible pavement construction/reconstruction cost for unit length of highway as it requires some distribution of trucks from the outside lane. Fuel consumption cost also decreases with increasing quantity and degree of truck platooning. Promotion of truck platooning by changing lane management policy approach increases flexible pavement rehabilitation cost to some extent but is a small fraction of the construction/reconstruction cost. Addition of a separate truck-only, platoon-only lane to the highway ensures further reduction in fuel consumption cost of the trucks. But a new lane would mean more cost for the construction, rehabilitation and right of way. Cost assessment for unit length of a six-lane highway with 8000 annual average daily truck traffic (AADTT) shows that the cost of fuel consumption reduction from the movement of truck platoons on the additional lane is higher than the combined yearly cost of construction, rehabilitation, and right of way for the additional lane. This suggests that there is financial incentive to consider tolled truck-only lanes in the future to promote truck platooning to its fullest possible extent.

This research shows a methodology to find out three important cost components (flexible pavement construction/reconstruction, rehabilitation, and fuel consumption) that would be largely affected if the lane management policy approach is updated for taking advantage of the connected and autonomous vehicles. Similar steps can be followed to find out if there is room for dynamically updating lane management approach in the future. A possible example of dynamic lane management approach would be allowing very limited truck platooning during the peak period on the outside lane of a multilane highway but allowing more truck platooning to take place on the inside lanes during the off peak hours. Another dynamic lane management approach example can be provided with the truck-only lane. The truck-only, platoon-only lane can accommodate some passenger cars during the peak hours and can again be made truck-exclusive for the rest of the day. Communication of such policy changes should be quite easy for future vehicles as they would be connected to each other and with the infrastructure. Probable cost trends for accommodating truck platoons in a highway segment have been reported here with one volume of trucks for a six-lane highway. Future studies can be conducted for different volume and lane configurations to understand the general nature of life cycle cost in large presence of connected and autonomous vehicles.

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