Congestion control (transportation)

Congestion control (transportation)
This article concerns road traffic. For telecommunications traffic, see congestion control.

Congestion control is a proposed alternative to congestion charging, which is used in a number of cities around the world (e.g. London congestion charge and the Singapore electronic road pricing). It aims to use the road to maximum efficiency while reducing user and system operating costs, when compared to the costs of congestion charging.[1]

It requires drivers to register for places within overlapping timeslots during rush hour, where each timeslot has a maximum capacity that is defined by the road network. Once capacity within a timeslot has been reached no new places can be booked (exceptions are made for emergencies). Any non-registered driver identified on the road at rush hour receives a fine similar to that of a speed camera ticket, where the fine is self financing.

Congestion control aim to reduce user and operating costs by using the fine size as a deterrent. With congestion charging all vehicles must be identified so that payment can be enforced. Thus cameras must be located at every entry/exit point. Congestion control operates in a similar way to that of automatic traffic surveillance, such as speed cameras. Drivers are aware there is a large fine to pay (£60+) for speeding and are warned in advance of the possibility of a camera. However, dummy cameras are used, as not every camera box site has a camera actually installed. As drivers do not know which camera boxes contain a camera they will have to assume each box contains a camera. This strategy reduces the infrastructure and operating costs. Congestion control operates in a similar way but is based on time and not speed. If the original London congestion charge operated 203 camera sites[2], congestion control could operate 150 (or less) with the obvious operational and maintenance savings.



At rush hour travelers drive within agreed timeslots (e.g. timeslots could be 6.30-7.30am, 7-8am, 7.30-8.30am, 8-9am and 8.30-9.30am). Where companies/schools and individuals register in advance for places within these timeslots. These are either on a one off ad-hoc or regular time basis. The ad-hoc places are allocated on a first come first serve rule and are free, while for regular places priority is given to specific jobs/roles/classes which don’t allow flexible hours (i.e. shop floor workers, hospital shifts or lesson start times). A local council or other controlling authority evenly distributes the registered traffic to the maximum capacity of each timeslot and the road network. Thus traffic load is evenly spread out during rush hour and at the optimum capacity of a road network without creating congestion (see figure 1 [3]).

Figure 1. Traffic load against morning rush hour, with and without congestion control.

To fit into the realities of life (e.g. due to leaving late for work) and avoid users speeding at the end of their regular slots, a set number of exceptions (e.g. 8) over a four week period are provided (note this does not apply to ad-hoc places). Each time the user is detected they receive a text message warning. If they exceed their allowance the user is charged every further time they are detected within another timeslots. On the assumption this happens at random the extra load should be evenly distributed over the four week period.


Two types of timeslots:

  • Ad-Hoc – for drivers who rarely need to use the road at rush hour but have a one off requirement (e.g. catching a flight)
  • Regular – daily commuters traveling to/from work/school, it is envisaged the majority are of this type (e.g. 90%)

Timeslot place are booked over the internet or by phone. However regular timeslots have to be requested and paid for on behalf of the individual by companies and schools. This payment can be passed onto the individual. However by taking the responsibility away from the individual, places are more likely to be canceled when not required. The monthly administration fee (fraction of the cost of monthly congestion charging commutes) required for the regular user pays for the booking service, while all other costs (e.g. fines issued, camera maintenance) are reclaimed by the fines.


(including costs and deployment) Enforcement is provided through RFID provide to Regular timeslot user and ANPR cameras. The cameras photograph number plate from car that are not detected by the RFID. The camera then compares the number plate with that of a timeslot list it has been sent before rush hour. If that number plate is not recognised a fine is issued.


  • Living within Congestion Control zone – People within the zone would be guaranteed an ad-hoc timeslots when required.
  • Job/lessons requiring specific timeslot – Priority on timeslot provision is given to those who’s job/schooling cannot have flexible hours
  • Unavoidable delay – (e.g. Bad weather, accidents delaying traffic), commuters may be delayed into the next timeslot. This would need to be at the discretion of the controlling road authority.
  • Emergencies – (e.g. Visit to Accident and Emergency) emergency services/hospitals are allowed to cancel individual fines
  • Vehicles – Emergency service vehicles, motorbikes, taxis and public transport


Congestion control aim to provide the following advantages over congestion charging:

  • Only drivers creating congestion pay
  • Reduced cost operating costs, thus reduce cost to users and the economy as a whole
  • Less infrastructure to maintain
  • Reduced/removed congestion and related reduction in CO2
  • Encourages companies to offer flexible hour polices to employees
  • Encourage use of public transport which is less restrictive on travel start times


Congestion control disadvantages when compared to congestion charging:

  • Congestion control is a theory and has not been proven
  • Restriction on private motor vehicle travel times during rush hour

See also


  1. ^ Thinking Highways ETC, Volume4, Issue 2, June-July 2009, Control not Charge, page 42 to 45.
  2. ^, accessed – 20th March 2009. Central London Congestion Charging Zone.
  3. ^ Department for Transport National Core Census - Traffic distribution by time of day on all roads: 2006

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