Road network

The road network is the system of interconnected roads designed to accommodate wheeled road going vehicles and pedestrian traffic.

Description

The road network consists of a system of interconnected paved carriageways which are designed to carry buses, cars and goods vehicles; the road network generally forms the most basic level of transport infrastructure within urban areas, and will link with all other areas, both within and beyond the boundaries of the urban area.

A road network can be divided into parts such as:

• intersections
  • controlled or uncontrolled intersections
  • roundabouts
• urban roads
• rural roads
• motorways
• bicycle lanes
• footpaths and pedestrian areas
• pedestrian crossings
• bridges, tunnels

Furthermore, several road-side systems (or Intelligent Transportation Systems, ITS) and monitoring systems are used to control the traffic, such as

• intersection control with traffic lights
• Variable Message Signs (VMS)
• Dynamic Road Information Panels (DRIPs)
• loop detectors

Functions

Social

The road network facilitates the movement of people allowing for social interaction. A high quality road network is essential not only for connecting key urban centres but for improving connectivity of more isolated local communities for whom many public transport options are limited or not available. Roads connect remote communities with the areas where employment options are more concentrated and services and facilities more readily available.

Economic

By connecting geographic locations, road networks facilitate the transport and movement of people, goods, and services, creating welfare. Road networks played a crucial role in the economic development of the 20th century, enabling relatively fast individual transportation for the masses from the second part of the 20th century. And although the development of air transportation and telecommunication networks started to compete with road networks during the later part of the 20th century, in most EU countries road transport still plays a crucial role in the national and local transportation networks.

Investments in road networks reduce the travel time between two locations, increase the robustness of the transportation network and hence reduce the travel costs. These kind of effects are referred to as the so-called direct effects of road networks. The economic impact of road networks extend in most cases beyond these direct effects due to the further rounds of economic activity as a result of the efficient transportation of goods, skills and persons, the so-called indirect economic effects. The investment in road networks, however, do not just lead to positive effects. Apart from the necessary investments in terms of time and money, road networks fill up land and have negative social and environmental impacts such as congestion, traffic accidents, light and noise pollution, and (of course) air pollution. In order to assess if an investment in a road network has a positive effect on society, or to compare different alternatives of transport infrastructure, economic tools can be used to value the positive and negative direct, indirect and external effects of these alternatives. The difficulty with this kind of economic appraisal is first of all that it is not easy to measure the valuation of travel time, and secondly that new road infrastructure will generate road use that would not have been made without the investments, the so-called induced demand. A third problem is that especially external effects such as quality of life, the value of unique nature, the value of no air pollution, are very difficult to be expressed in monetary terms.

Although road networks are hardly affected by security threats (crime, terrorism), it can happen that roads get blocked due to e.g. riots, bomb explosions, traffic flow management, etc. The economic impact of these kind of threats can be significant, especially in indirect terms since roads facilitate economic activities. Security measures can prevent these negative economic effects, for instance, by ensuring there are alternatives routes for traffic (traffic flow management). These security measures, however, also generate economic impact, especially when these measures limit the mobility of road users. See the case example below:

In economic terms, checkpoints help to apprehend persons in violation of laws and confiscate contraband (such as smuggling goods). The benefits of checkpoints can be quantified in terms of the number of apprehensions per patrol agent. Some detailed studies suggest that checkpoints have a positive benefit-cost ratio. Take for example a study on the community sobriety checkpoint program estimated benefits from the National Highway Traffic safety Administration (NHTSA). This report states that for every $1 spent on sobriety checkpoint program the community saves more than $6, including $1.30 of insurer costs(Miller et al., 1998).. Nevertheless, screening of persons also generates indirect costs that are generally hard to measure. Think of effects such as delays (for both private persons as commercial transportation companies), inconvenience for travellers, and the quality of life for local residents. On top of that, checkpoints may possibly also raise concerns about the overall safety of the region, influencing economic activities such as tourism and local business customer ship.

According to the results of SeRoN(a project funded by the European Community), actions to protect road bridges and tunnels against terrorist threats are rarely cost-effective. The researchers concluded this based on a developed software tool that helps transport operators to decide where to invest in security, ranking infrastructural objects according to their importance in terms of traffic volume, damage potential, reconstruction time and symbolic value. Nevertheless, the project coordinator stresses that with additional safety or traffic management effects, investment in highway security might be cost-effective, especially if also social and political views are taken into account.

Mobility

The function of a road network is to facilitate movement from one area to another. As such, it has an important role to play in the urban environment to facilitate mobility. It furthermore determines the accessibility of an (urban) area (together with public transport options).

The capacity of a network is determined by its roads. The capacity of a road is the maximum number of vehicles that can pass a certain road section per hour. The capacity of a road is determined e.g. by its width, number of lanes and speed limit. If the traffic demand is larger than the road capacity, congestion will occur. When congestion is present, the road network cannot longer fullfill its task. Therefore, one tries to prevent or reduce congestion with traffic management measures.

Developing a good road network has many positive effects, such as stimulating the development of certain areas (commercial activities, urban development, creating jobs etc.). For security, good accessibility by the road network is also important, for example for good accessibility in case of incidents (see also incident management). However, the road network may also facilitate criminals to reach their target. This could be controlled with access control.

Safety

Safety of road users is typically focused on road safety (prevention of accidents through speed control, seatbelt enforcement, etc).

Proper planning is critical in ensuring road safety: In the case of national roads, where the speed limit can exceed 50-60 km per hour, the proliferation of roadside development should be avoided. The intensification of or the development of new accesses to national routes can generate additional turning movements which in turn can introduce additional safety risks to road users.

The lay-out of the road should help to improve traffic safety, for example by providing seperate bicycle lanes and physically seperated driving directions for motorways and larger urban roads. In The Netherlands one uses a uniform lay-out for different road types which should help to increase recognizability and safety .

Security Issues

The presence or absence of routes from one place to another can influence the mobility of the public, but also of criminals. This can have a direct effect on the perceived attractiveness of a location to criminals. Security issues influence by the pervasiveness of the road network because an easy escape adds to the attractiveness of targets, are:

• Burglary
• Robbery
• Raid
• Vehicle theft

The layout of the road network and its associated potential to ram a car through a window front is essential to the attractiveness of objects for

• ram-raiding

Disturbance of important traffic nodes can attract a lot of public attention. This can make these nodes (like important or prominent bridges or tunnels) attractive objects for

• destruction of property by fanatics

Measures

The measures for each type of security issue can be found on the respective pages. There are few measures that are specifically suited or unsuited to this kind of urban object, but some general considerations can be mentioned:

• Directing traffic flows and access control should only be taken if it doesn't hamper the primary function of the road network, providing mobility, too much.