Clear zone and Horizontal Clearance.pptx

traffic engineering

1. Clear zone and Horizontal Clearance Geometric Design of Transportation Facilities Assignment-3

2. CLEAR ZONE (Roadside Design Guide) A Clear Zone is an unobstructed, traversable roadside area that allows a driver to stop safely, or regain control of a vehicle that has left the roadway. A clear zone as the total roadside border area, starting at the edge of the traveled way, available for safe use by errant vehicles. This area may consist of a shoulder, a recoverable slope, a non-recoverable slope, and/or a clear run-out area.

3. CLEAR ZONE (Roadside Design Guide) Simply stated, it is an unobstructed, relatively flat area beyond the edge of the traveled way that allows a driver to stop safely or regain control of a vehicle that leaves the traveled way. A recoverable slope is a slope on which a motorist may, to a greater or lesser extent, retain or regain control of a vehicle by slowing or stopping. Slopes flatter than 1V:4H are generally considered recoverable.

4. CLEAR ZONE (Roadside Design Guide) A non-recoverable slope is a slope which is considered traversable but on which an errant vehicle will continue to the bottom. Embankment slopes between 1V:3H and 1V:4H may be considered traversable but non-recoverable if they are smooth and free of fixed objects. A clear run-out area is the area at the toe of a non-recoverable slope available for safe use by an errant vehicle. Slopes steeper than 1V:3H are not considered traversable and are not considered part of the clear zone .

5. Roadside Design Guide By creating Clear Zones, roadway agencies can increase the likelihood that a roadway departure results in a safe recovery rather than a crash, and mitigate the severity of crashes that do occur. ** Since the recovery is less likely in steeper slopes, no fixed object should be present in the vicinity of the toe of these slope.

6. Clear Zone at horizontal curves

7. Horizontal Clearance Horizontal clearance is the distance between extreme edge of carriageway/vehicle to the face of nearest obstruction or support. Horizontal clearance is the lateral offset distance from the edge of the traveled way, shoulder or other designated point to a vertical roadside element(Roadside Design Guide). This clearance will ensure safety of the vehicle and helps the vehicle to travel at design speed. Underpass (IRC 54) Rural Roads : Single Carriageway Desirably the full roadway width at the approaches should be carried through the underpass. This implies that the minimum lateral clearance on either side must equal the shoulder width. This rule should be relaxed only in exceptional circumstances.

8. Horizontal Clearance Category of road Normal case (m) Exceptional case (m) NH AND SH 2.5 2 MDR AND ODR 2 1.5 VILLAGE ROAD 1.5 1.0 If footpath is provided than it shall be equal to width of footpath plus 1 m W1 = Lateral Clearance W2 = Footpath Width

9. Horizontal Clearance Rural roads Divided Carriageway Left side clearance of vehicle is same as that of single carriageway system. Right side *0.5 m of side safety margin is added in case of Kerbed central median. Kerb Provision Desirable (m) Exceptional (m) No 2.0 1.0 Yes 1.5 + 0.5* 1.0 + 0.5*

10. Horizontal Clearance W3 = Right Lateral Clearance without kerb . W4 = Right Lateral Clearance with kerb . W5 = Side safety margin (extra carriageway width to offset kerb shyness)

11. Horizontal Clearance Urban Roads Single Carriageway In case of kerbed section with a footpath, the kerb shyness of 0.25 m on lower category of roads (Collector and local streets) and 0.5 m on high category of roads (Arterial and sub-arterial) shall be provided(side safety margin). If footpath is not provided , then the lateral clearance of 0.5 m on lower category of roads and 1.0 m on high category of roads shall be provided from the edge of the pier/abutment(L2).

12. Divided Carriageway Left side clearance shall be as per single carriageway system Right side clearance It shall be 1.0 m on higher category of roads and 0.5 m on lower category of roads from the edge of median/pier (L4). Horizontal Clearance

13. Horizontal Clearance for Electrical Installation (IRC 32) Horizontal clearance is the horizontal distance, measured at right angles to road alignment, between roadway or carriageway edge and a pole carrying an overhead utility line, or any polesupporting structure. Poles carrying overhead power and telecommunication lines shall, excepting the urban areas, be erected at least 10.0 metres away from the nearest edge of the roadway, provided also that these are at a minimum distance of 5.0 metres from the nearest line of avenue trees. In case of roads having, at present, a narrower roadway than that prescribed in the standards in force this horizontal clearance shall be reckoned from what will be the ultimate edge of the roadway after widening to the said standards. The standards for horizontal clearance laid down above shall not apply to roads situated in mountainous country. In such areas, poles should be erected preferably on the valley side, and as far away from the edge of the road as practicable .

14. The horizontal clearances in respect of poles erected for the purpose of street lighting shall be as under(Also apply in case of urban areas) .

15. Horizontal Clearance If the median is not wide enough to allow such clearances, then it should be either widened near the approaches to the underpass or single span structure should be provided omitting the need of central pier .

16. References https://www.fhwa.dot.gov/programadmin/clearzone.cfm?_gl=1*tx3yu4*_ga*MTE4OTE5MTI1OS4xNjkyMDkwNjk2*_ga_VW1SFWJKBB*MTY5ODcyNzY3OC40LjEuMTY5ODczMDYxNy4wLjAuMA . Highway Design Manual(Chapter 10),Roadside Design, March 2020. IRC 54 Guidelines. IRC 32 Guidelines.