Transportation creates places. The means of production and the creation of wealth are typically concentrated in places that allow convenient transportation of materials, people, and goods. Transportation brings people and goods together, and the locations where commerce and culture are exchanged inevitably draw more people. Human settlements first clustered around seaports and waterways; today's new urban developments typically revolve around useful roadways*.
Changes in the way people use roads and changes in the physical road network are linked to the shape of urban development. The separation of residential, shopping, and employment areas through zoning increases the distances citizens must travel on a daily basis. As automobile ownership and mobility has increased over the last fifty years, many destinations have migrated from city centers to the outskirts where land is cheaper, thus allowing larger parking lots, larger stores, and larger home lots at lower cost. Municipalities may extend water and sewer services to these areas in order to promote economic growth and collect increased tax revenue. The new locations usually benefit from an economy of scale, siphoning customers, jobs, and investment away from urban centers. The expansion of these land uses into the urban fringe often draws high volumes of traffic onto rural roadways that were originally designed only for very light volumes of farm-to-market traffic. The resulting traffic in these areas makes conditions less safe or pleasant for pedestrians and bicyclists who want to travel to the same destinations.
Many cities have added new freeways around their outer perimeters in order to allow inter-state traffic to bypass congested city highways and link together new developments in the urban fringe. Unfortunately, these goals are often at odds with one another. The convenience of the new freeway usually accelerates growth at the outer edge of the city; eventually this growth can induce enough traffic to create new congestion problems. Meanwhile, the new growth occurs in low-density patterns on previously rural roads that were not designed to handle high volumes of mixed urban traffic. This creates increased difficulties for pedestrians and cyclists who live, work, and shop in those areas, limiting cycling and walking to those few who lack cars or are highly dedicated to non-motorized travel modes. When the roads are upgraded to mitigate traffic, new travel lanes are added but little or no consideration is typically given to pedestrians and cyclists due to their low volumes under the existing conditions. Sidewalks, pedestrian signals, and wide outside lanes are often omitted from road designs in the suburban fringe even as new destinations attract large numbers of people.
When rapid suburban expansion occurs without consideration of the impact on pedestrians and cyclists, the resulting road network can be difficult and expensive to retrofit to universal access later. Low development density and wider separation of uses means higher costs of sidewalk construction normalized per pedestrian trip. Strip development along suburban thoroughfares may make it difficult for pedestrians to cross wide multi-lane roads, but owners of frontage property may resist the installation of raised center medians or refuge islands that may block direct vehicle access to their driveways from the opposite side of the street. Property owners may also resist the construction of wide outside lanes or sidewalks that require a wider right-of-way. Some suburban thoroughfares feature high-speed interchanges and free-flow intersections that can be especially challenging to redesign for safe passage by pedestrians. Some important safety modifications may effect reductions in motor vehicle speed, which will not be appreciated by motorists who are accustomed to traveling long distances in a shorter time. On very wide multi-lane suburban roads, adding adequate pedestrian clearance time to traffic signals can increase delays for motorists or decrease roadway capacity. Efforts to serve suburban areas with mass transit are more expensive and less successful where pedestrian access is unsafe, uncomfortable, or inconvenient.
By planning ahead, many of these problems can be avoided. A proper balance of land use planning and transportation planning can be accomplished with the aid of the following strategies:
1. Pace the annexation of land and extension of water, sewer, and other services into rural areas with facility upgrades so that all public streets are universally accessible. Require that new urban land uses be contiguous with compatible and complementary land uses and connected by streets meeting universal access criteria. Upgrade important arterial and collector roads with sidewalks as motor traffic increases. Provide wide outside lanes in areas where traffic volumes and speeds make it more awkward for drivers of motor vehicles to move into the adjacent lane to pass cyclists.
2. Avoid serving undeveloped areas with convenient freeway or high-speed arterial access until secondary roads in those areas can be upgraded to provide universal access under the motor traffic volumes and urban growth that the new facility will induce.
3. Plan major suburban intersections for the inevitability of pedestrian and bicyclist traffic between developments at all four corners of the intersection. Avoid widening roads where longer pedestrian clearance intervals will create unacceptable delays for vehicle traffic.
4. Use raised center medians and refuge islands on roads wider than three lanes, especially if distances between intersections are long or traffic speeds are fast. Avoid strip development or excessive driveways and access points on roads wider than three lanes or without center medians. Avoid widening roads with frequent driveways and intersections beyond three lanes unless raised center medians will be used to provide safe refuge for pedestrians crossing the street.
5. Cluster complementary land uses (such as residential and activity centers) in close proximity, and provide redundant connections. Avoid requiring travelers to use arterial roads for every trip to the store or school. This reduces traffic on arterials and improves conditions for those who make short trips.
6. Provide a mixture of residential housing types near major employment centers. Ensure that roads between employment centers and nearby residences are universally accessible.
*or railways, in those situations where railway travel competes effectively with roadway travel. Railway travel has a stronger effect on land use where motor vehicle travel is constrained by price and availability of parking or roadway resources, or by government intervention.