THE HOLLAND TUNNEL GRAY AND HAGEN 583 



when the first was outfrrown, the obvious proceeding; was to construct 

 a 2-liue tunnel and when its capacity is reached, to build another 

 2-line tunnel at some other location as determined by future traflio 

 conditions. The Holland Tunnel is, therefore, a twin-tube tunnel, 

 providing in each tube for two lines of traffic in each direction. 



In planning the entrances and exits of the tunnel, a careful study 

 was made of veliicular traffic, with particular reference to its move- 

 ment at street intersections ami through the tunnel. It was recog- 

 nized that wherever traflic intersects, its continuity is broken. In- 

 stead of moving in a steady stream, it breaks into a series of waves 

 as it is held up and released at intersections. This interruption in 

 the stream of traffic at street intersections so limits the capacity of a 

 street that its real capacity as determined by its width is never 

 reached. 



A tunnel differs from a street in that the only interruptions by 

 cross traffic are at the entrances and exits. Consequently these 

 points are of vital importance, affecting as they do the ultimate ca- 

 pacity of the tunnel. Unless the entrances and exits insure con- 

 tinuity of traffic during the period of maximum demand, the 

 capacity of the tunnel roadway can never be reached. 



Accordingly, the entrances and exits of the Holland Tunnel are 

 widely separated. In New York Cit}', one is to the north and the 

 other to the south of the Canal Street through traffic; in addition 

 they are located so as to be served by two main north and south 

 avenues. Tunnel traffic is thus given the best iDossible facility for 

 free movement while at the same time the greatest separation is se- 

 cured at a reasonable cost. In accord with this same principle the 

 entrance and exit at the Jersey City end are located in separate 

 streets adjacent to the railroad yards east of the north and south 

 traffic streets connecting Jersey City with Hoboken. 



This separation of the tunnel entrance and exit traffic is consid- 

 ered to be a factor of the greatest importance in relieving congestion 

 in the vicinity of the tunnel. This was particularly necessary in 

 New York City, with its large and rapidly increasing volume of 

 traffic. It was also called for in Jersey City, where there were no 

 wide thoroughfares in the vicinity of the tunnel. 



In addition, property was taken to provide broad plazas at en- 

 trances and exits. The entrance plazas serve to accommodate the 

 waves of traffic as they approach the tunnel and converge in the 

 portal roadway into continuous lines of vehicles through the tunnel. 

 Similarly wide exit plazas insure the free and uninterrupted move- 

 ment of traffic away from the tunnel. Through the .separation of 

 entrance from exit, and the use of adequate plazas, the tunnel traffic 

 can bo distributed over a large number of streets. 



