Signage is another important element of urban shuttle-lane roadworks as it provides drivers with warnings about oncoming hazards or change of road layout. The Department for Transport (2011) sets the required signs and their setting distances for each type of shuttle- lane roadworks based on previous research. Failure to comply with the design standards will create unnecessary risks to drivers. Table 4.27 lists the required signs at each type of shuttle- lane roadworks.
According to the Department for Transport (2011), the minimum and normal maximum setting distance for the first sign in advance of the lead-in taper (first cone) should be between 20 and 45 metres. It also states that all signs should be visible to approaching drivers with a minimum clear visibility of the first sign at 60 metres.
For shuttle-lane roadworks controlled by temporary traffic signals, signs 1 to 6 should be used. For Give/Take operation, signs 1, 3 and 4 only should be used. For priority operation, signs 1, 3, 4, 6 and 7 should be used. All signs should be placed according to the Department for Transport (2011).
Tables 4.28 and 4.29 summarise the observed signage for each site and each stream with their setting distances and comparing each direction to the design standards. Sites 1, 8, 9, 10 and 15 are not included in the table as they are not shuttle-lane roadworks sites (i.e. signalised junction or traffic calming sites).
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Table 4.27: List of sign for shuttle-lane roadworks Sign
Number Sign Description
1 Roadworks ahead
2 Traffic signals ahead (if site is operated by temporary traffic light)
3
Road narrows on left hand side (used in primary stream) Road narrows on right hand side (used in secondary stream) 4 Where vehicles should stop at temporary traffic signals
4
Keep right, keep left
6 End of roadworks
7
Give way to oncoming vehicles Priority over oncoming vehicles
It can be seen from Tables 4.28 and 4.29 that placing signs at roadworks were not carried out correctly according to the design standards at most of the sites. At some sites (i.e. sites 7, 12, 13 and 14), there were missing signs which can cause confusion to drivers approaching the roadworks site and may result in an increase in the risk of collision due to driver hesitation or sudden braking.
It was also observed at most sites (i.e. sites 2 to 7, 11, 14, 15, 78, 18 and19) that signs were not placed according to the recommended design standards (signs should be placed at a distance between 25-50 metres from the first cone). It was also observed that not all signs were visible to drivers at most of the sites (columns 7 in Tables 4.28 and 4.29), were signs were either covered by parked vehicles or had been knocked down.
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Table 4.28: Signs and distances for historical roadworks sites
Site Dir. Are all signs available Missing signs Distance to first sign (m) According to standards Are all signs clear to oncoming traffic 2 P - 260 S - 285 3 P - 89 S - 102 4 P - 187 S - 142 5 P - 95 S - 110 6 P - 70 S - 92 7 P 1,2,3 21 S all 26
Table 4.29: Signs and distances for current roadworks sites
Site Dir. Are all signs available Missing signs Distance to first sign (m) According to standards Are all signs clear to oncoming traffic 11 P - 55 S - 68 12 P 1,3 40 S - 44 13 P 1,7 25 S 1,3 20 14 P - 30 S all 0 16 P - 54 S - 42 17 P - 89 S - 114 18 P - 93 S - 99 19 P - 54 S - 42 20 P - 65 S - 52 21 P - 32 S - 28 22 P - 59 S - 47 23 P - 48 S - 30
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4.13Summary
This chapter presented the data analysis stage which is performed on the data collected from shuttle-lane roadworks sites and other various sources. The analysed data was used in developing, calibrating and validating the micro-simulation model as described in Chapter 5 and 6.
Video recordings for over 54 hours (23 sites) were used to analyse the various information of shuttle-lane roadworks.
Video recordings were used to extract various sets of information such as flow level and profile, following headway (close following “tailgating”), Move-up time (MUT) and Move-up delay (MUD).
Data taken from over 5.3 million IVD data records were used to calculate car length and model the probability distribution of car length. HGVs data collected from both visited sites and manufacturer catalogues of vehicles and were used to calculate the HGVs length and distribution.
Signals type and settings were collected and analysed using video recordings and onsite observations.
Drivers’ compliance with temporary traffic signals was collected using video recordings. Information regarding drivers’ compliance included drivers crossing through amber and red light violations per cycle.
Site observations using a measuring wheel were used to collect signage information and distances at all shuttle-lane roadworks sites.
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CHAPTER FIVE:
LIMITATIONS OF THE S-PARAMICS
MICRO-SIMULATION MODEL
5.1
Introduction
The current chapter describes the development process of the S-Paramics micro-simulation model for studying urban roadworks and specifically, shuttle-lane roadworks operated by temporary traffic signals. The chapter also describes the calibration, validation and limitations of the S-Paramics micro-simulation model.
S-Paramics is a micro-simulation software package capable of representing the behaviour and interaction between individual vehicles on the road network. Different road layouts and features may be simulated and drivers’ behaviour characteristics can be changed relatively easily as part of the calibration and validation of the model to replicate actual site observations.
The S-Paramics also provides outputs and presents real-time visual displays for various traffic management and road network designs. Vehicle dynamics (i.e. acceleration and deceleration rates and vehicle dimensions) can also be changed to represent real observations (SIAS Limited, 2007). In the current study, the S-Paramics 2010.1 was used to develop, calibrate and validate shuttle-lane urban roadworks micro-simulation model operated by FT signals as discussed in the following sub-sections.