Source: adapted from Barber, G. (1995) “Aggregate Characteristics of Urban Travel”, in S. Hanson (ed) The Geography of Urban Transportation, 2nd Edition, New York: The Guilford Press, p. 92.
The above figure is a typical representation of urban travel by purpose and by the time of the day in North American cities. It depicts the daily share of each trip by purpose by the time of the day. There are two prevalent peak hours corresponding to home-to-work trips, the morning peak hour around 8h00 (18.5% of all daily work trips), and the afternoon peak hour around 17h00 (13.5% of all daily work trips). Shopping trips mostly occur during the afternoon (11.4% of all daily shopping trips taking place around noon), while social and recreational trips are mainly occurring in the evening (17.5% of all social and recreational trips taking place around 21h00). This unequal distribution of movements is often creating congestion during peak hours since the demand will likely exceed the capacity of the urban transport system. Three major strategies can be implemented to alleviate this problem:
- Flexible Work. Altering the times at which people are arriving and leaving work would level out the distribution of trips. For several activities such as retailing this strategy is difficult to implement since they require synchronized work shifts and fixed opening hours.
- Land Use Modifications. Changing the distribution of employment to alleviate traffic in most congested areas and spread the traffic around. Since the 1950s, several activities have been relocated in suburban areas, notably nearby highway interchanges. However, in several instances, this only increased or moved congestion problems elsewhere. Further, the distribution of employment is influenced by economic and accessibility factors.
- Constraining Transport. Private cars can be denied access to some areas, such as the central business district, or tolls (congestion pricing) can be used to influence behavior. In a number of cities, traffic is getting increasingly controlled, but these measures are usually not highly effective.
Therefore, in spite of possible mitigation strategies, the distribution of urban trips by the time of day has not changed much.