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Dedicated Roadways Can Benefit Even Level 5 Automated Transit Vehicles

November 24th, 2017


by Robert Johnson

Automated passenger vehicles such as people movers at airports currently operate on exclusive guideways. In some systems, the guideway mechanically constrains the vehicles, while in others it is simply an ordinary road set aside for the exclusive use of the vehicles. Examples of the latter type include the Ultra system at London’s Heathrow airport and the 2getthere system at Masdar City, Abu Dhabi.

Because of recent advances in software and hardware, automated vehicles (AVs) will soon be able to operate in mixed traffic along with conventionally driven cars, pedestrians, and cyclists. At that point, costly infrastructure will be unnecessary and automated taxis and buses could use existing streets. However, even if an AV were capable of SAE Level 5 operation (automated operation in every situation a human driver could manage), there can still be significant benefits to providing it with an exclusive roadway. In many cases, it will be more cost effective to increase the capacity of a freeway or arterial by adding exclusive lanes for an AV system, rather than conventional lanes open to all vehicles.

The benefits include:

• Exclusive lanes for an AV system can be much narrower than conventional lanes. Less side clearance is needed because AVs can steer precisely, and if the vehicles were part of a fleet they could be uniformly narrow. For example, the Ultra vehicle needs a lane only 160 cm (5.3 ft) wide.

• Less than half as much vertical clearance is needed as for a conventional lane. Only about 2 meters of clearance (6.6 ft) should be adequate for vehicles with all seated passengers. This allows grade separation at greatly reduced cost. In areas of moderate density with a limited number of cross streets, the AV road could be mostly at grade and pass under cross streets in a structure similar to a pedestrian underpass. Pedestrians and cyclists could cross the AV road at points between cross streets by using small bridges. The AV road could drop to about 1 meter (3.3 ft) below grade under the bridge, thus allowing the bridge surface to be slightly more than 1 meter above grade.

• The support structure for elevated sections of an AV road would be much lighter and less expensive than for an equivalent length of conventional roadway, since the latter must be able to carry heavy trucks.

• Accidents caused by manually driven vehicles would be eliminated, greatly increasing safety and eliminating delays that even a minor accident can cause.

• Because of much lower local environmental impact, AV roads could be routed through areas where a conventional road would be unacceptable. Public opposition to new freeways and even arterials is well known. In particular, nearby residents object to noise and pollution from internal combustion engines. If the roadway were part of an AV system, residents could be assured that all vehicles would be electric, and there would be no noise from revving engines, honking horns, squealing tires, or large trucks.

Most of the benefits mentioned above are greatest for systems using narrow vehicles with all seated passengers. The same benefits are present, but to a lesser degree, for larger automated shuttles that accommodate standees, such as the 2getthere ParkShuttle and the EasyMile and Navya shuttles. These are higher and wider than Ultra vehicles, but can still use exclusive lanes that are narrower and have less vertical clearance than is required for conventional traffic.