Part 9: Level crossings

Last updated: December 2008. This document ceases to be a controlled document when printed. Please refer to the current version at www.landtransport.govt.nz

Appendix B - Sight distances at level crossings

B1    Introduction

Appendix B describes the formulae and parameters used to assess sight distance available at level crossings.

The design vehicles adopted for these calculations are:

• the maximum length vehicle generally able to use New Zealand roads without special conditions, namely 20 m; or
• the maximum ‘design vehicle’, which is set at 25 m (vehicles greater than 20 m may use roads subject to conditions described in Land Transport Rule: Vehicle Dimensions and Mass 2002, which also requires vehicles over 25 m long to have written permission from the rail access provider to cross any level crossing); or
• the maximum length single unit vehicle (truck or bus) able to use New Zealand roads without special conditions, namely 12.6 m.

Vehicle stopping, start-up and clearance parameters used for each of these vehicles are listed in table B1. The vehicle dimensions and performance characteristics used in these procedures are subject to change if new information becomes available.

When assessing sight distances at level crossings, views obstructed by permanent features such as terrain and buildings should be clearly distinguished from views obstructed by growth such as hedges or fencing. It is always preferable to remove view obstructions than install Stop controls at crossings. The Railways Act 2005 gives the railway access provider powers to remove or lower trees, hedges and walls that obstruct level crossing views.

B2    Approach visibility

A road vehicle driver approaching a level crossing with a ‘Give Way’ (RP2) sign needs to be able to either:

• see an oncoming train in time to stop before reaching the level crossing; or
• continue at the approach speed and cross the level crossing safely ahead of a previously unseen train or a train far enough away to be clearly not a collision threat.

The required sight triangles to achieve this, shown diagrammatically in figure B1, are calculated as follows:

(a)   Vehicle stops after seeing train and before reaching the level crossing

The value of S1, the minimum distance of an approaching road vehicle from the nearest rail at which the driver must be able to see an approaching train from either direction in time to stop if necessary before reaching the level crossing, ie to stop at the Give Way line, is given by:

where

Other notations are described in figure B1.

(b)   Vehicle able to continue at speed and cross safely before train reaches level crossing

The sight triangle requirements are given by S₁ and S₂ in figure B1.

The value of S₁ is the same as in (a).

The value of S₂, the minimum distance at which the road vehicle driver needs to be able to see the train approaching from either direction in order to cross safely ahead of it, is given by:

where

Other notations are defined in equation (1) or described in figure B1.

A train, if present, needs to be visible to a road vehicle driver between any two points within the sight triangle.

B3    Restart view

A road vehicle driver when stopped at the Stop line needs to be able to see far enough along the railway to be able to start off, cross and clear the level crossing safely before the arrival of any previously unseen train. The required sight triangles to achieve this are shown diagrammatically in figure B2.

Distance S₃ is the minimum distance at which an approaching train from either direction must be seen in order for the design vehicle to start off and clear the level crossing by the safety margin shown in figure B2. Distance S₃ is given by the following:

where

Other notations are described in figure B2.

B4    Sighting angles

In order to ensure a motor vehicle driver can see along the prescribed sight triangles without excessive head movement or sight obstruction by parts of the vehicle itself, the following maximum sighting angles shown in figure B1 and figure B2, measured from the direction of travel of the vehicle at the point or points at which sightings must be made, should be available:

(a)   Maximum angles when approaching Give Way controlled level crossings

• (i)   to the left (X_1L) – 95 degrees
• (ii)   to the right (X_1R) – 110 degrees

(b)   Maximum angles when approaching Stop controlled level crossings

• (i)   to the left (X_2L) – 110 degrees
• (ii)   to the right (X_2R) – 140 degrees

For the purpose of calculating sight triangles, the following figures are used:

• distance from driver’s eye to the nearest rail when stopped at the Stop line – 5 m
• height of driver’s eye above road level – 1.0 m
• height of train headlight above rails – 2.6 m.

B5    Vehicle deceleration factors

The value ‘d’, the coefficient of deceleration, in equations (1), (2) and (3) is the uniform deceleration rate for a vehicle approaching a level crossing that may be required to stop on the approach due to the presence of a train and is given in table B3.

Table B1  Vehicle stopping, start-up and clearance parameters

Vehicle type (see B1)	BT(s)	J(s)	L(m)	a (m/s2)
Maximum length vehicle	1.0	2.0	20.0	0.36
Maximum ‘design’ vehicle	1.0	2.0	25.0	0.36

Table B2  Grade correction factors

Grade (m/m)	Grade correction factor (Gs)
-0.12	0.52
-0.10	0.57
-0.08	0.63
-0.06	0.70
-0.04	0.79
-0.02	0.88
0.00	1.00
0.02	1.12
0.04	1.25
0.06	1.39
0.08	1.54
0.10	1.69
0.12	1.85

Table B3  Coefficient of deceleration for road vehicles (trucks)

Vehicle speed (km/h)	Coefficient of deceleration (d)
< 95	0.29
95-105	0.28

Figure B1  Approach visibility at passive controlled level crossings

Position 1(i) - Driver approaching level crossing sights train, judges that a stop is needed, decelerates and stops at the limit line.

Position 1(ii) - Driver approaching the level crossing either cannot see approaching train or sights train too far distant to be a collision threat, continues at speed and crosses ahead of the train.

Legend   (general case assumptions are shown in brackets):

Figure B2  Crossing visibility at passive controlled level crossings

A motorist stopped at a level crossing requires adequate time to accelerate and safely clear the level crossing.

Legend   (general case assumptions are shown in brackets):

B6    Pedestrian sight distances

At a level crossing where there is no active control for either roadway or pedestrian traffic, for a train approaching from either direction, the sight distance (SD) in metres to oncoming trains to enable pedestrians to cross safely is as follows:

where

B7    Example view lines

Table B4 provides some example outcomes from equations 2, 3 and 4 based on differing train speeds, vehicle lengths or pedestrian safety margins, and incorporates some typical values for the other parameters used.

Table B4  Examples based on equations 2, 3 and 4

Train speed VT (km/h)	Restart view S3 (m)		Approach visibility S2 (m)		Pedestrian view SD (m)
	Vehicle length L		Vehicle length L		Safety margin t
	12.6 m	25 m	12.6 m	25 m	0 sec	2 sec
40	149	179	97	121	65	87
70	261	313	169	213	114	153
80	298	358	193	243	130	175
100	373	448	242	304	163	219
110	410	492	266	334	179	240

The notations and parameters used for these calculated distances are described in table B5 below.

Table B5  Notations and parameters used in calculations for values for table B4

Parameter	Notation and values
highest authorised train approach speed	VT
view along the railway line at 5 m from nearest rail	S3
minimum view along the railway line at 30 m from the nearest rail based on a driver approaching the level crossing slowing to 20 km/h	S2
desirable view along the railway line at 4 m from the nearest rail for all pedestrian level crossings, unless automatic warning devices have been installed	SD
assumed safety margin between a train arriving and the pedestrian clearing the limit line on the departure side of the level crossing	t sec
vehicle lengths	L = 12.6 m
	L = 25 m
approach grade	G = 0
deceleration rate of truck (d)	0.29
perception plus reaction time	2.5 sec (RT)
brake delay	1.0 sec (BT)
start-off time (including brake delay)	2.0 sec (J)
vehicle acceleration across crossing	0.36 m/sec2 (a)
vehicle 85th percentile speed	20 km/h
set back limit line from nearest line	3.0 m
driver’s eye from front of vehicle	2.0 m
distance a pedestrian walks	8.0 m (PD)
pedestrian walking speed	1.0 m/s (PS)

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