Butzek-troemel roundabout or "spiralabout"

Abstract

The proposed design of the Butzek-Troemel Roundabout, or spiralabout, provides a number of substantial improvements over traditional multilane roundabout design principles. By providing a generally outward spiraling lane design instead of a continuously circulating lane design, approach capacity, departure capacity, and circulating lane utilization are all enhanced. Vehicle conflict points are reduced compared to standard roundabout designs with as many approach lanes, thus improving safety. The design provides a viable alternative to traffic signals at significant multilane intersections, and an improvement on the roundabout, an emerging design concept in the United States.

We claim as the invention the following:  
     
         1 . Geometric design principle involving shift of circulating lanes outward by way of the addition of lanes on the inside and the forcing of outside lanes toward the departures.  
     
     
         2 . Geometric design principle typically moving vehicles out of the roundabout within one revolution.  
     
     
         3 . Geometric design principle aiding drivers in being in the appropriate lane for their destination and discouraging traffic from remaining in the circle longer than necessary by way of exit-only lanes.  
     
     
         4 . Additional approach capacity provided by allowing one more approach lane than circulating lane by way of a lane addition on the inside of the circle.  
     
     
         5 . Enhancement of utility or value of internal circulating lane(s), as each lane directs vehicles toward a departure that would be considered logical to an entering driver (i.e. a right turn, through, left turn, or U-turn movement).  
     
     
         6 . Flexibility in design to allow for modifications to basic design providing additional vehicle capacity for specific movements through the addition of approach and circulating lanes, as necessary (examples of which are shown in FIGS.  4 - 6 ).