Traffic congestion and urbanization

Traffic congestion is a situation in which demand for road space exceeds supply.

Traffic congestion is the impedance vehicles impose on each other, due to the speed-flow relationship, in conditions where the use of a transport system approaches capacity. Traffic congestion is essentially a relative phenomenon that is linked to the difference between the roadway system performance that users expect and how the system actually performs.

Cities and traffic have developed hand-in-hand since the earliest large human settlements. The same forces that draw inhabitants to congregate in large urban areas also lead to sometimes intolerable levels of traffic congestion on urban streets and thorough fares.

Urban traffic congestion must be understood in the wider context of city dynamics and agglomeration benefits. Traffic congestion in urban areas is often the outcome of successful urban economic development, employment, housing and cultural, policies that make people want to live and work relatively close to each other and attract firms to benefit from the gains in productivity thus derived. There are many indications that, even though they may not be thrilled by the prospect, urban road users are prepared to live with crowded roads so long as they derive other benefits from living and working in their cities.

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Traffic congestion prevents us from moving freely and it slows and otherwise disrupts the conduct of business within urban areas. However, it is important to note that unfettered movement is not the primary benefit we derive from living in urban areas. Cities provide access to a wide range of activities, people, services, goods, markets, opportunities, ideas and networks. These benefits can be delivered either through speed or through greater proximity. Congestion may affect travel speed but in some circumstances, such as dense urban cores, congestion may both be expected, and to some degree accepted. In these cases, cities have come to accept a degree of congestion and continue to get along relatively well as long as overall accessibility is high.

It is difficult to see how congestion can or should be eradicated in economically buoyant urban areas nor is there any indication that urban road users expect to travel in congestion-free conditions at peak hours. This is not to say that cities like Lagos should not proactively and vigorously address growing congestion – they should, especially in cases where congestion can be linked to specific traffic bottlenecks.

We can say that traffic congestion is excessive when people say it is but this does not account for what it would cost to bring congestion back down to levels that are tolerable. Though, urban roads are not built to deliver free-flow speeds 24 hours a day, 7 days a week, 365 days a year albeit traffic congestion should not be never-ending tale of woes.

Traffic congestion has an impact on both the speed of travel and on the reliability of travel conditions. It is the latter that may be of greatest concern to individuals and businesses.

Congestion is increasing in many urban areas across the country and in locations where populations and city economies are growing, it is likely to continue to increase. However, it is not clear that traffic congestion is rising equally fast across all areas in the country, nor that the rise in traffic has followed the same patterns and has been caused by the same phenomena. In many cases, congestion has grown as cities have grown and as economic activity has expanded. Cities have grown as they attracted more people and activities, they have produced more wealth and, as a by-product, their roads have become more crowded. Traffic congestion has grown in absolute terms in many areas but in some cases, it may not necessarily have grown in relative terms as measured by unit of economic output or per capita.

In one respect, the relative rise in traffic congestion can also be seen as a “natural” consequence of the “lumpy” nature of infrastructure provision. The proximate causes of traffic congestion are numerous, e.g. too many vehicles for a given road’s design or intersection capacity, dynamic changes in roadway capacity caused by lane-switching and car-following behaviour, road accidents and high vehicular movement of heavy duty vehicles.

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They are also invariably linked to other indirect factors such as land-use patterns, employment patterns, income levels, car ownership trends, infrastructure investment, regional economic dynamics, etc…

In view of the a fore-mentioned premise there are two types of traffic congestion; Recurrent and Non-recurrent.

When roads are operated at or near their maximum capacity, small changes in available capacity due to such factors as differential vehicle speeds, lane changes, and acceleration and deceleration cycles can trigger a sudden switch from flowing to stop-and-go traffic. Likewise, saturated intersections can quickly give rise to queues whose upstream propagation can swamp local roads and intersections.When this occurs then we have a situation called recurrent traffic congestion

Non-recurrent congestion on the other hand is the effect of unexpected, unplanned or large events (e.g. road works, crashes, special events and so on) that affect parts of the transportation system more or less randomly, and as such, cannot be easily predicted. The share of non-recurrent congestion varies from road network to road network and is linked to the presence and effectiveness of incident response strategies, roadwork scheduling and prevailing atmospheric conditions (rain, fog, etc.).

Finally, effective congestion management policies should seek to understand the nature of travel demand in congested conditions. While commuting trips may be a key factor, it is important not to overlook other types of peak-hour trips including school runs, leisure travel and freight travel that often make a substantial contribution to traffic in peak periods.

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