|Road (automobiles, buses, trucks)||None to limited||Congestion.|
Operational safety (speed limits).
Limited access highways.
|Rail (Freight)||Limited||Operational safety (grade crossings).|
Availability of train slots.
|Rail (Passengers)||Good to significant||Development of high speed rail systems.|
Long term potential of new technologies (e.g. Maglev).
|Air||None to limited||Energy consumption.|
Congestion at airport terminals.
Abandonment of supersonic services.
|Maritime||None to limited||Energy consumption (slow steaming).|
Transport improvements have conventionally been linked with improvements in speed as better engines and vehicles were designed and as infrastructure was built to handle faster operations. However, the last half-century has seen for several modes little progress. Although the core reasons behind this are related to energy consumption and technical limits, each mode has specific considerations about potential speed improvements:
- Road. Although there are limited technical considerations to increase vehicle speed, safety considerations limit the operational speed. Most drivers would not be capable of operating vehicles at speeds above 120 km/hr for highways and above 60 km/hr on urban roads. Speed limits are in part imposed to ensure an acceptable safe operating level for most drivers as well as to mitigate energy consumption. The only option to break this limitation would be automatically driven vehicles over specific road segments (e.g. limited access highways), but this would require information technology infrastructures that are unlikely to be available in the near future. Additionally, congestion is becoming more acute, particularly around the world’s major metropolitan areas, mitigating potential speed improvement benefits. Still, as observed after the construction of the interstate highway in the United States, the setting of a system of limited-access highways is linked with notable average speed improvements at the national level.
- Rail (freight). Outside energy consumption considerations, which are significant, there are several factors limiting speed improvements for freight trains. One concerns grade crossings where much faster freight trains would require a complete separation of road and rail traffic with the significant infrastructure investments this would entail (e.g. overpasses). The other relates to the availability of train slots along corridors as a unit train occupies a specific capacity. Faster trains would imply fewer available slots. Intermodal train speed is also mitigated by the capacity of terminals to handle the operations that a higher frequency of train arrivals and departures would imply.
- Rail (passengers). The development of high-speed rail systems underlines the substantial potential for speed improvements for passenger rail services. At the regional level, such services are able to compete with air transport effectively. The prospects of new technologies such as maglev indicate that there may be additional potential for speed improvements with fixed rail systems but would require significant capital investments.
- Air transport. For air transport, marginal speed improvements make little difference on short to medium distances since these services are more influenced by airport congestion than air travel speeds. Congestion at airports has incited airlines to post longer flight times than in previous decades. For long-distance travel, where speed improvements would make a difference, energy consumption issues are a serious impediment since they would reduce the range of the aircraft. In some cases, such as transatlantic services, the timeframe can be convenient for passengers. For instance, on the American East Coast, flights bound to Western Europe usually leave in the evening to arrive early in the morning on the next day. Commercial supersonic jet services have been abandoned because they proved to be difficult to justify financially. Therefore, technical improvements in air transport are mostly geared towards lowering energy consumption.
- Maritime. The prospects of speed improvements for commercial maritime transportation are minimal. While hull design and coatings enhancements have been significant, like for air transport, the focus has been to reduce energy consumption, not to improve speed. Higher energy prices, namely bunker fuel, have incited several maritime shipping companies to implement slow steaming practices along several commercial routes. A large share of global maritime container shipping is thus running at slower speeds. Still, there is for passenger transportation, and possibly for niche freight markets, the potential of operating at higher speeds. For instance, fast ferries can be used to service high-density short distances in passenger markets.
Therefore in such a context, future improvements in the fluidity of transportation are much less likely to be derived from speed but from efficient and interconnected operations.