Text d. Characteristics of highway traffic.

Read the text and say how traffic intensity varies.

Vehicles traveling in the same direction constitute traffic stream. It is apparent that the greater the number of vehicles in a stream, the more severe will be the requirements to be satisfied by the road.

A traffic stream usually consists of many types of vehicles, traveling at different speeds and carrying various loads. However in order to determine the width of the carriageways and the overall width of the road, the total number of vehicles on the road at a given period is taken as the major design criterion.

The total number of vehicles passing through any section of a road in unit time (day, hour) is called the traffic intensity. Traffic intensity varies along each individual road section; it increases in the vicinity of towns, large inhabited localities and railway stations and is reduced along stretches of road some considerable distance from large towns and cities. The traffic intensity on a road does not remain uniform throughout the day. It decreases sharply at nightfall.

Traffic intensity is not the only basic traffic characteristic. To determine the pavement thickness and to design different structures one has to know not only the number of loads but also their wheel loads and overall dimensions of vehicles.

The maximum wheel loads and overall dimensions of single and combination vehicles are established the by State Standards.

Single and combination vehicles are divided into two groups. Group A includes vehicles operating on roads of classes I and II with improved pavements as well as on roads of other classes if they are specially designed for such vehicles. Group В includes all other single and combination vehicles.

All vehicles whose weight when loaded exceeds 1,5 tons must have wheels with pneumatic tyres, with a mean unit load on the pavement of not over 6,5 kg/cm2 for group A and 5,5 kg/cm2 for group B.

Theory and practice show that a heavy-weight vehicle at one pass can do more damage to a road than the passage of a great number of lighter vehicles.

Section II. Grammar

1. Подготовиться к лексико-грамматическому тесту по текстам:

Test 1.Functional classification of highways. Test 2. Freeway.

2. Повторить грамматический материал к лексико-грамматическому тесту:

1. Видо-временные формы глагола:

а) активный залог - формы Indefinite (Present, Past, Future); формы Continuous (Present, Past, Future);

формы Perfect (Present, Past, Future);

б) пассивный залог - формы Indefinite (Present, Past, Future). Особенности перевода пассивных конструкций на русский язык.

2. Модальные глаголы:

а) выражающие возможность;

can (could), may и эквивалент глагола can - to be able to;

б) выражающие долженствование:

must, его эквиваленты to have to и to be to; should.

3. Простые неличные формы глагола:

Participle I (Present Participle), Participle II (Past Participle) в функциях определения и обстоятельства