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��Z� 2-20 Sight distance on the crest of a hill is the distance at which a driver can see an objecttwo feet above the road. �r:�,��►i ��yC��L�� li��'�� U ��? t � � t s � Y � �� x��.s � f � �� � � � �u�.� ��a � 9 � �:��.�� +�f��r�€ �.5� i�''P 32 Residential Streets Object Height 2.0' � _ �+'�H1Fd�Jl� R�4TE OF �ERF��L CURVATURE Design Speed (�ph? 15 20 25 30 35 40 45 Stopping Sight Distance (feet)' 80 115 155 200 250 305 360 Ewe ��nr �.�� Rate of ��s�N�ai Curvature KZ Crest Curves Saq Curves 3 10 7 17 12 26 19 37 29 49 44 64 61 79 '�+a�+�Fl haa��M1e�,lyt�4jr. rJ �.5 kY. +iil,�i�cS }+�/'� M, Irrl ' f�4r�+e��oNt�e t� p�k*�ql�l�[�+tVY�+��k� dr�+oe Yefr�ei �q�� 5n�,�kai k�vori� af��"�'�� OIG�.�F�irFar�A�c��`4'r+v� +��'lkl��h4�►�°f�� 4 �A F�Ft�43,'r�+r�d3,�Ylh�.}6r�.�r.iqL� Vertical curve length should be a minimum of 50 feet. When the algebraic dif- ference in grades is less than � percent, no vertical curve is necessary for local residentia! streets. Horizontal Curves Horizontal curves on low-speed residential streets should not use supere3eva- tion (banking) to counteract centrifugal force on the vehicle; the design should allow centrifugal force to be counteracted solely with side friction from the pavement (Figures 221 and 2-22). Table 2-8 summarizes guidelines for the length of the centerline radius in horizontal curves. If centerline radii are in- creased, driver comfort will be enhanced. But frequently, the decision to length- en curve radii has adverse consequencessuch as the loss of natural terrain. trees, and watercourses and an increase in vehicle speeds. Dead-End 7"urn�r�urtd� On most dead�nd streets, a circular turnaround area is preferable (Figure 2-23). AT- or Y-shapedturnaround may be used for streets having a short length, al- leys, and streets serving up to ten houses (Fiqure 2-24). Extremelyshort streets serving no more than five houses may not require a turnaround: vehicles may simply use the street width for backingfturn�ng movements.