Highway Research Record

Environmental Capacity of Urban Transport Networks

Date of Start:July 2004
Civil Engineering Department, Indian Institute of Technology, Roorkee (R, I)

Scope and Objective
(i) To appreciate the state of art in air pollution due to vehicle emissions.
(ii) To study the parameters affecting the pollutant concentration in air.
(iii) To develop the environmental capacity norms of urban roads.
(iv) To appreciate the role of environmental capacity norms in transport policy guidelines and to strengthen the need of       adequate public transport (9).

The environmental capacity of a road stretch varies as one considers different type of impacts. Environmental capacity of urban roads will restrict the maximum number vehicles plying on a particular type of road. It needs to restrain the volume of traffic in order to maintain environmental standards. Increased use of motor vehicles particularly heavy commercial traffic, two and three wheeler traffic due to increased urban activities have put up great pressure on the road network of our cities, leading to congestion and pollution.
The concept of environmental capacity is a quantifiable systematic technique and it develops a relation between the environmental parameters and the transportation network features. The criteria chosen to define this relationship are noise, odors, air pollution, vibration, dirt and litter, damage to vegetation, pedestrian safety and conflicts with movement patterns on the road. The environmental capacity will depends upon characteristics of the road itself, it’s design speed, no. of lanes and their widths, no. of feeding roads in the stretch, composition of the traffic especially heavy vehicles.
In this study, an attempt has been made to study the various air quality models and to predict the carbon monoxide concentration has been done for all the twenty selected locations of Delhi using CALINE-4 and General Finite Line Source Model. Speed-flow curves were developed by using GFLS model, from this the environmental capacity was obtained by super imposing another speed-flow curve (enveloping curve) from CRRI.
The environmental capacity in terms of traffic noise was also calculated for the five selected locations of Delhi. The attitudinal survey of residents was done for getting the environmental score.

Findings and Conclusions
(i) Speeds have a very significant relationship with the exhaust emission of a vehicle. Low speed of traffic particularly in central     areas of Indian cities in mainly responsible for the automobile pollution.
(ii) Model, for estimating ambient concentration of pollutant can be used for long term prediction for transport environmental     planning and management decisions.
(iii) Till today no technique has been evolved to express capacity in terms of noise level. Environmental capacity of these road      stretches will provide us the upper limit of traffic volume that could be permitted without exceeding the allowable noise      level.
(iv) The reason for annoyance is low background noise level. So, the sudden increase of noise level due to low traffic volume       moving with high speed is sufficient to make people annoyed. The speed reducing devices like speed breakers can reduce       the speed which could make the area comfortable.
(v) Even at the increased traffic in peak hour in central areas, environmental capacity shows very less proportion of available      capacity. This will also help in making the present noisy roads to friendly roads by knowing that how much traffic has to be      reduced on these roads.
(vi) The study environmental capacity of different road stretches passing through various residential areas have been useful in        predicting maximum acceptable traffic which passes through a residential areas with comfortable to the residential areas       with comfort to the residents living that area.
(vii) The wide pavements that would greatly improve the environment of the street, through doubtless in practice some space       would have to be allocated for grouped lay-bys for parking.

In the transport planning process, study strongly recommends that at the stage of assignment as well as modal split, environmental capacity norms should be followed. Depending upon the different areas of the city environmental capacity of roads will be different and this will ensure safe environmental in a city. Environmental capacity analysis will ensure sustainable development of cities free from noise and air pollution.