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What is the importance of glass beads in road markings?

Retroreflectivity refers to the part of incident light from headlights of a vehicle being reflected back to the driver. Retroreflectivity is normally achieved in road marking materials by using glass beads or ceramic beads.

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These beads are sprayed on the marking materials when the road is marked. The beads are transparent and serve as lenses. When the light passes through the beads, it is refracted through the beads and then reflected back towards the original path of entry. The use of glass beads enhances retroreflectivity which raises the safety level for night driving.

glass-bead-on-roads

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

What is the purpose of road studs in roads?

In nighttime, car drivers could not see where the road ends and where the alignment of road changes in direction. Without sufficient number of road lightings, it is necessary to provide some means to guide the drivers along dark roads. Hence, in 1933 Percy Shaw invented the cat’s eye (i.e. road studs) which is based on the principle of cat’s eyes. When a ray of light enters the eyes of a cat, the light shall be reflected back towards to the emitting source. As such, with the reflection of car’s headlights by road studs, it is possible to identify road conditions and alignment in darkness.

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However, the provision of cats’ eye is not without problem. For instance, there have been reported accidents arising from loosely installed cat’s eye. Some new design of cat’s eye uses LEDs which flash at about 100 times per second. However, it is claimed to cause epileptic fits of drivers.

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

Are kerbs necessary in road pavements?

In general, kerbs are essential in road pavements due to the following reasons (based on Arthur Wignall, Peter S. Kendrick and Roy Ancil):

(i) They provide strength to the sides of road pavements and avoid lateral displacement of carriageway due to traffic loads.

(ii) In terms of road safety, they serve as a separation line between footway and carriageway and aid car drivers in driving safely.

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(iii) They act as a vertical barrier to guide the surface runoff collected in road pavements to the gullies.

gully-granting

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

What is the difference between sag gully and on-grade gully?

A sag gully is a gully installed at a low point in roads and stormwater would pond up the gully. An on-grade gully is a gully installed in a sloping road where any excess flows may bypass the inlet and flow to another one downstream. Generally speaking, the entry capacity of sag gully can be estimated from hydraulic design. But for on-grade gully, owing to complicated hydraulic behaviour, the entry capacity can hardly be predicted in accuracy by mere calculation.

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This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

When should horizontal bars and vertical bars be provided in kerb overflow weirs?

Overflow weirs should be provided for steep roads (longitudinal gradient>5%) , flat roads (longitudinal gradient<0.5%), sag points and blockage blackspots. For steep roads, flow is rapid and overflow weirs should be provided to accommodate the excess flow. For flat roads, the probability of accumulation of rubbish increases. Therefore, overflow weirs should be provided in these locations to bypass the stormwater flow in case of blockage of gullies caused by trapping of rubbish. [wp_ad_camp_1] Basically, kerb overflow weirs suffer from the drawback that it provides another passage for debris to enter the gullies and therefore bars (either horizontal or vertical) should be provided to prevent the entry of debris into the weirs. For steep roads, as the main concern is to provide an alternative route for excess flow, horizontal bars should be provided in this case to maintain better drainage efficiency. For flat roads, the purpose of overflow weirs is to trap rubbish and therefore, vertical bars should be provided because it is more effective in prevention of entry of debris. This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.