CHAPTER 2 BARRIER WARRANTS

Barrier Warrants ________ November 2005Table 2.1: Clear Zone Distances from Edge of Through Traveled WayDESIGNSPEEDDESIGNADT20 mph Under 750750 - 15001500 - 6000over 600025 - 30mphUnder 750750 - 15001500 - 6000over 600035 mph Under 750750 - 15001500 - 6000over 6000(Continued) (U.S. Customary Units)FORESLOPES1V: 6H 1V: 5H 1V: 3H 1V: 3H 1V: 5Hor flatter toto1V: 4H1V: 4H2 - 63 - 75 - 87 - 103 - 75 - 87 - 107 - 105 - 87 - 1010 - 1212 - 143 – 75 - 86 - 107 - 105 – 86 - 107 - 1010 - 126 – 107 - 1212 - 1414 - 16******2 - 62 - 63 - 75 - 82 - 63 - 75 - 87 - 103 - 75 - 87 - 1010 - 12BACKSLOPES2 - 62 - 63 - 75 - 82 - 63 - 75 - 87 - 103 - 75 - 87 - 1010 - 121V: 6Hor flatter3 - 73 - 75 - 87 - 103 - 75 - 87 - 107 - 105 - 87 - 1010 - 1212 - 14* See the AASHTO Roadside Design Guide for design speeds 40 mph and higher.** Foreslopes between 1V: 4H and 1V: 3H are traversable but non-recoverable. Since vehicleswill not reduce speed or change direction on these slopes the needed clear zone is determinedby the slopes above and below the non-recoverable slope and extended by the width of the nonrecoverableslope. See Chapter 3 of the RDG for more information on this procedure.Foreslopes steeper than 1V: 3H are considered hazards.2.2.3 Horizontal Curve AdjustmentOn the outside of horizontal curves errant vehicles are likely to leave the roadwaytangent to the curve. Consequently, additional clear zone is needed for recovery. Table3.2 of the RDG suggests multipliers for adjusting clear zones on the outside of horizontalcurves. The RDG recommends that this adjustment be used where there is reason toexpect the curve to be a concern. A crash history, inadequate superelevation andserious hazards within the adjusted clear zone may be reasons to consider using anadjusted clear zone. Since roadside crashes are more likely to occur on the outside ofhorizontal curves, the use of these adjustments should always be considered.Adjustments on the inside of horizontal curves are not appropriate. Table 2.2 expandsthe RDG table to account for lower speeds.________________________________________________________________________2-4 Determine the Needed Clear Zone