Road Tapers

[1989hf]

Hi,

I'm new to this forum and quite new to highway design too. My question is regarding hatched road tapers and how to work them out. For instance, I have a 3m island and need hatched taper coming out of this on a 30mph road. I've found in DMRB that the taper should be 1:40 so does that mean for every 40ms down, you go in one meter and then join the line from the origin to this point? If so, the lines will not meet at 40m so do you extend to a point where they do? Or should I consider it 1.5:60 as my island is 3m wide? Any help would be much appreciated.

 

[CivilEngAus]

Your state road authority should detail what their line marking requirements are. In saying that however, 40m total length for the speed seems acceptable. The taper starts at 1.5m wide (assuming the island is centred on the control line of the road) and goes down to nothing (0m wide) 40m up the road, i.e. this would be a 1:26 taper.

If your road authority requires a 1:40 taper then you lose 1m of width for every 40m of length. Assuming as above the 3m wide base island is central on the control line (centreline), then you need to lose 1.5m of width, i.e. 1.5 * 40 = 60m long taper required. A taper down to zero is seldom practical so you might use double lines there instead.

I would suggest putting a tapering nose on the end of your island if possible rather it being simply 3m wide at the end the island. Particularly if you are deflecting the traffic lane and forcing a driver to navigate around the island.