Stockholm bypass tunnel - Merging traffic study. Technical report

Projekt:

Kunskapscentrum vid VTI för Virtual Prototyping

Sammanfattning:
The Stockholm bypass (FS) project is a new road project that will create a bypass of central Stockholm. The entire project includes motorways, bridges and two tunnels; one of which will be 16.5 km. The Stockholm bypass is the largest infrastructure project in Sweden to date. A high level of road traffic safety is always important and when the road is in a tunnel, and especially in a long tunnel, maintaining the highest possible level of safety is paramount. The present report describes a simulator study on the merging of traffic from entry ramps into the main tunnel. The entry ramps in the Stockholm bypass tunnel are planned to let traffic merge in to the main tunnel from five specified locations, (excluding the main southbound and northbound entrances).

The present study focused upon the specific situation of driving down the on-ramps and entering (merging) in to the main tunnel with a special emphasis on measures of safety and driver performance. A group of 21 participants, 11 males and 10 females, were recruited from the VTI participant database. They were instructed to drive a series of test scenarios in a 3D-model of the Stockholm bypass tunnel in the VTI driving simulator III. There was simulated traffic on the main tunnel to improve the realism for the participants merging from the entry-tunnel ramp on to the main tunnel. Two gap sizes were used. The gap sizes between vehicles on the main tunnel were relatively small. The gap sizes are not intended to represent mean values that allude to total traffic intensity. They are however, gap sizes that road users will observe on a daily basis when using the E4 motorway through Stockholm and this is the rationale for using relatively small gap sizes because they reflect real-life traffic situations. Pre-, peri- and post-measures of driver performance (speed, time headway, vehicle position and distance to tunnel wall etc.) and the CR10 subjective judgements of the driving task (with four dimensions) were administered inside the simulator between conditions. The study design was a within-subject design where all of the participants drove all of the four included experimental conditions.

The main results of this study suggest that the merging zones were too short for some of the participants to merge comfortably and safely. The merging zones are found at the point where the entry-ramp tunnel merges with main motorway tunnel and comprise an observation section, an adjustment section and a completion (/taper) section. The distance-to-wall measure (the measure that gauges how much of the entry-ramp remains at the time of merge-completion) for the Vinsta (0.5 km) ramp with heavy traffic is particularly concerning from a road traffic safety perspective because more than 25 % of the participants completed the merging manoeuvre with less than two seconds of time-headway (THW) remaining before the end of the completion section.

In order to establish the causes and to seek and verify possible solutions to the safety concerns arising from this study, a number of areas need to be explored. Would for instance, lengthening the merging zone at Vinsta improve the safety of that entry ramp? What are the characteristics of a tunnel motorway entry-ramp that gives provision for safe and well-working merging? On the other hand, what causes unsafe merging performance? Could it be other aspects apart from the actual length of the merging zones? Moreover, only two of the five entry ramps have been assessed in this study. What is the status of the remaining entry ramps from a safety perspective? It is also important to investigate the effects of heavy traffic (buses and trucks) on interaction with other road users and merging.



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Författare: Patten, C., Mårdh, S. och Ceci, R.
Utgivare: Statens Väg och Transportforskningsinstitut (VTI) - ViP Publication 2014-3
Utgivningsdatum: 2014-07-15
Diarienummer: TRV 2010/2237
Antal sidor: 43
Språk: Engelska
Kontaktperson: Ruggero Ceci, PLa2tvu
Beställ från: Statens Väg och Transportforskningsinstitut (VTI)