Not sure about Environmental Engineering but I would say that Chemical Engineering has allowed vehicles to be lighter (with the use of specific plastics and polymers). Chemical Engineering has enabled to develop such new materials used in transport, but also new alternative fuels, which have a different environmental impact, this is where Environmental and Chemical Engineering come together.

"Green" nanocomposites are being developed these last years, such as nanocellulose, which have remarkable properties and could be a substitute for plastics. Take a look at this article : http://www.acs.org/content/acs/en/pressroom/newsreleases/2011/march/green-cars-could-be-made-from-pineapples-and-bananas.html

Generally speaking, environmental engineer should do environmental impact assessment for any project including the transportation systems, participating in planning phase, risk assessment studies, nature protection, and sustainability. as any new project has direct impact on environment and Eco system. As we considering autonomous car many questions will rise such as is there any special services for such cars? Any extra infra structure? How do they interact with environment and its elements? Lastly, Environmental engineering is related to civil engineering in educational levels so both can have many overlaps.

On the other hand, chemical engineers can participate in control systems for example controlling the combustion rate of fuel; develop more efficient fuel types for autonomous cars.

When thinking about environmental engineering in the transport sector remember that vehicles need surfaces to drive upon and that such surfaces generate polluted run-off when it rains.

It is part of  the role of an environmental engineer to deal with both quality and quantity (flooding) issues arising from such sources.

The major environmental problem from transport sector is the issue of pollution that emanate from the sector. The role of environmental engineering with respect to the transport sector  would have to be in the area of pollution reduction. So, it can be factored into road designs and automobiles engine designs in such a way that pollution would be minimized.

For the transport sector, chemical and environmental engineering seeks to continuously reduce the quantity of chemical pollutants released directly and indirectly into the environment, as well as putting measures in place to ensure the safety of users of all forms of transport, in order to ensure continuous sustainability.

In the transport sector, chemical engineers have contributed greatly in the designing of more efficient engines that produce fewer hazardous pollutants, they have helped reduce the environmental impact of gasoline and fuel powered cars, buses, and trucks.