Transportation Engineering

Road Classification & Capacity 1

COURSE : DCEB 2FT MODULE : TRANSPORTATION ENGINEERING MODULE NO : BE 7601 TOPIC ONE : ROAD CLASSIFICATIONS _____________________________________________

AIMS

1 To know the importance of road classifications.

2 To understand the various elements of roads and their functions.

3 To know the characteristics of different types of roads.

4 To be able to compute the capacity of a roadway.

1. INTRODUCTION

This lecture is about different types of roads and their functions. The students need to realise the importance of road classification in planning.

1.1 ROAD ELEMENTS

The following road elements are found in almost all modern roads and each have their own function in promoting safety, traffic efficiency and maintainability.

a) Traffic lane channelizes and guides the traffic

b) Carriageway the pavement surface on which traffic travel c) Kerb the raised edge of the road. This defines the edge of the

carriageway and also helps restrains vehicles from running into pedestrians or oncoming vehicles in the event of an accident.

d) Foot path Provided along the side of most roads so that pedestrians do not stray onto the carriageways

e) Shoulder 3m strips on the sides of expressways for emergency stops and for access by rescue vehicles.

f) Camber / Crossfall - Cross slope for drainage of rain water and also to assist car in making turns

g) Central divider / Centre median Space or barrier provided between opposite traffic lanes to separate vehicles travelling in opposite directions.

h) Road side drain To drain away rainfall so that flooding does not occur.

Figure 1 A typical arterial road in Singapore. Can you identify the road elements this picture?

1.2 CLASSIFICATION OF ROADS

Roads are classified into the following four categories:

a) Expressways b) Arterials. c) Primary Access

Advantages and Disadvantages of Roadside Trees

Roadside trees are not necessary for transportation purpose and are in fact a hazard in three ways they block the view of the drivers, they are a collision hazard and leaves falling off the trees adversely affect the braking resistance of cars.

However, trees make the streetscape more pleasant and are a benefit overall.

Transportation Engineering

Road Classification & Capacity 2