Eye and object heights

The sight distance available is dependent on the eye height of the observer which in United Kingdom practice is taken as 1:05 m. This inevitably represents a compromise as anthropo­metric measurements and vehicle di­mensions will vary considerably. The minimum height selected for the object is also important and ideally should be the minimum detail discer­nible by, at least, the average visual acuity, for the given speed and vie­wing conditions.

The principal control in the design of summit curves is the sight distance requirement. Two conditions arise which depend on whether the vertical curve is longer or shorter than the speci­fied sight distance. Because large earthwork cuttings may be needed for the establishment of safe passing sight distances it is frequently the case that the shorter safe stopping sight distances are adopted for economic rea­sons.

Riding comfort. The effect of travelling over a summit curve is to give an apparent loss of weight and, on a sag curve, an apparent increase due to the centripetal acceleration.

Sight distances at junctions. The operation of junctions is affected by the sight distances allowed for approaching drivers and the relative and absolute speeds of the vehicle manoeuvres. Priority junctions are the simplest form of mandatory control and are either of the Give Way (or yield) type and those requiring the side-road vehicle to stop at the major road.

In the case of Give Way junctions it is necessary for a driver approaching on the minor road to have a sufficiently long length of the intersecting road in view to enable him to assess the major road traffic situation, and to make a decision whether to cross or not. A view far enough back along the ap­proach is needed to enable a stop to be made at the junction, if required.

Where there is a STOP control on the side road of the junction a halted driver must have time to perceive the traffic situation, decide to cross (perception-reaction time) and accelerate from the stopped position to clear the junction (acceleration time).

TEXT-BASED ASSIGNMENTS

Ι. Translate into Ukrainian: eye height, compromise, anthropo­metric measurements, vehicle di­mensions, acuity, summit curves, sag curve, centripetal acceleration, junction, mandatory, major road, minor road, acce­lerate, to clear the junction, traffic situation.

ΙΙ. Choose English equivalents:

1. спостерігач a) observer b) arrangement c) organization

2. розміри a) detail b) di­mensions c) consume

3. гострість a) acuity b) search c) examine

4. крива a) crane b) curve c) cater

5. причина a) rea­son b) respect c) attitude

6. перехрестя a) jump b) junction c) point

7. обов’язковий a) regular b) main c) mandatory

8. усвідомлювати a) perceive b) enable c) achieve

9. прискорення a) acquire b) acceleration c) accident

10. оцінювати a) evident b) apparent c) assess

ΙΙΙ. Match words from columns A and B to make word-combinations:

A B

1. eye a) junction

2. summit b) control

3. anthropometric c) road

4. earthwork d) reasons

5. visual e) acceleration

6. economic f) acuity

7. centripetal g) curve

8. mandatory h) cuttings

9. side i) height

10. priority j) measurements

ΙV. Decide whether the statements are true or not. Correct the wrong ones:

1. The sight distance available is not dependent on the eye height of the observer.

2. The minimum height selected for the object is also important.

3. Three conditions arise which depend on whether the vertical curve is longer or shorter than the speci­fied sight distance.

4. The effect of travelling over a summit curve is to give an apparent loss of weight.

5. The operation of junctions is not affected by the sight distances allowed for approaching drivers and the relative and absolute speeds of the vehicle manoeuvres.

6. Priority junctions are the simplest form of mandatory control.

7. In the case of Give Way junctions it is necessary for a driver approaching on the major road to have a sufficiently long length of the intersecting road in view to enable him to assess the major road traffic situation, and to make a decision whether to cross or not.

8. Where there is a STOP control on the side road of the junction a halted driver must have time to perceive the traffic situation.