Urban road networks and ring road

Forms of urban road network

1. Grid-iron (rectangular): parallel roads cross at right angles.

  |   |   |   |
--+---+---+---+--
  |   |   |   |
--+---+---+---+--

Simple and flexible, but many conflict points and long diagonal trips.

2. Radial (star): roads spread from the central business district (CBD) like spokes.

     \  |  /
   ---- O ----
     /  |  \

Gives direct access to the centre but causes congestion there.

3. Radial-circular (ring-radial): radials joined by one or more ring roads.

    .-----------.
   /   \  |  /   \
  |  ---- O ----  |
   \   /  |  \   /
    '-----------'

4. Hexagonal: three-way junctions only; fewer conflicts but difficult to set out.

5. Linear (ribbon): development along one main axis (e.g. a highway or river).

6. Irregular/organic: grows with the terrain and history, as in old Kathmandu valley towns.

How a ring road reduces congestion in the city core

A ring road is a circumferential road around the city that connects the radial roads outside the central area.

1. Diverts through traffic: vehicles which only pass the city (trucks, inter-city buses) use the ring instead of entering the core.
2. Links radial roads directly, so traffic going from one suburb to another need not pass through the centre.
3. Reduces vehicles, noise and pollution in the CBD and gives space for pedestrians and public transport.
4. Improves access to the outskirts and helps controlled development of the city fringe.
5. Gives a high-speed alternative route and reduces travel time and accidents.
6. Helps freight movement: heavy vehicles can be restricted in the centre in day time.

Example: the Kathmandu Ring Road (about 27 km) carries traffic around the old city and the core.