1. - ericssonhistory.com

Traffic Signals at Vasterbron, StockholmBENGT VON MATER N, THE STOCKHOLM TOWN BUILDING OFFICEU.D.C. 656.056(487.1)L M Ericsson's vehicle controlled traffic signals have been earlier describedin Ericsson Review Nos. 3/1950, 1/1951 and 2:1955. The present articlecontains an account of the traffic control installation, with many interestingfeatures, at the Langholmsplan intersection on the approach to Vasterbron inStockholm. In particular a new method of varying the maximum green periods,so providing several signal programmes, is described.Traffic signals of L M Ericsson make were installed at Langholmsplan onthe south side of the Vasterbron Bridge in Stockholm in August 1956. Vasterbronis the only north-south bridge west of the city and has to carry increasingquantities of traffic. At present some 45.000 motor vehicles and trams cross thebridge every day, and at rush hours it is used to maximum capacity. Thisheavy volume of traffic obliged the municipal authorities to widen the bridgeto six lanes and to reconstruct Langholmsplan at its southern abutment.Layout of LangholmsplanLangholmsplan was earlier formed as a roundabout, which meant thatright-turning traffic caused considerable stoppage. Since its reconstruction intoa signal-controlled crossing with right-turn prohibition, and simultaneouswidening of the bridge, the traffic flows more smoothly. The present layoutis shown in fig. 1. It is seen that the tramway has a large stopping place inthe centre of the intersection. Signals are located at three points: at thejunction of Langholmsgatan—Hogalidsgatan. and at two pedestrian crossingswith push button operation on the east and west of the tram stop. An internallylit "No Right Turn" sign is presented to traffic coming from Vasterbron.Vehicles intending to turn right from that direction are instead directedleft immediately after the bridge abutment and take a newly built road underthe bridge leading to the western part of Sodermalm. Traffic from the oppositedirection is likewise forbidden to swing direct right into Hogalidsgatan.But such traffic is rare and is allowed to turn at point a (fig. 1).Three Interconnected InstallationsThe three signal installations are interconnected, the larger constituting themaster installation (/) with the two others (2 and 3) dependent on it.If no demand has been registered from pedestrian push buttons at 2 and 3,signals at / operate as a normal two-phase system whereas traffic passingsignals at 2 and 3 has right-of-way. Two-way traffic movement takes place onLangholmsgatan during phase A, and on Hogalidsgatan—which has tworight-turn lanes leading onto the bridge—during phase D. The interplaybetween / and 2 is evinced if a pedestrian has required passage at 2. Signalsat 2 thereupon follow the changes at / in the sense that the red aspect is pre-