Defensive Driving Rules

Note- this tab is only available on Loader simulations

SimSig has built-in generic defensive driving rules. These try to replicate a typical driver who, rather than waiting to the last possible moment to brake and coming to a stop exactly at a red signal, would slow down in stages - particularly when passing a single yellow signal (meaning the next signal should be expected to be red).

Custom defensive driving rules allow the timetable creator to more closely represent a particular train operating company's driving rules. This is because the rules vary between different companies, resulting in different behaviours.

These rules only exist in simulations using the SimSig Loader. They are not available in standalone .exe simulations.

Defensive Driving Set

A defensive driving set contains a number of rules grouped together. Typically one set would represent one train operating company - for example, Thameslink.

Defensive Driving Rule

A defensive driving rule specifies the behaviour for a single rule. A number of parameters are required or optional:

Aspect: This determines whether the rule applies for a particular aspect. When a train passes a signal, it remembers the aspect it just passed. This is the aspect used for this rule. For example, set to Y for this rule to apply to trains that have just passed a single yellow signal. Banner repeaters and shunt signals in preset shunt mode are ignored for this purpose, but ordinary distants and repeaters do apply.
From linespeed: This determines the minimum speed to which the rule applies. If the train is travelling below this speed then the rule does not apply. Note that if the train accelerates to or beyond this speed then the rule will activate.
To linespeed: This determines the maximum speed for which the rule applies. If the value is zero then no maximum applies. If the train is travelling faster than the specified speed (and that value is not zero) then the rule will not apply. However, if the train slows down below this value then the rule will activate.
Reduce to: In combination with the adjacent "Type", this specifies the absolute speed or the percentage of linespeed that the train will travel at, at a maximum. For example, if "Type" is Absolute and the value is 40 then the train will not exceed 40mph. If "Type" is Percent, the value is 67, and the linespeed is 90mph, then the train will not exceed 60mph.
Type: As indicated above, possible values are Percent and Absolute, plus N/A (not applicable). The latter will prevent this section applying.
Approach next: In combination with the adjacent "Type", this specifies at what speed, or percentage of speed, to approach the next signal at.
Distance: In combination with "Approach Next", this indicates the distance from the next signal that the "approach next" applies.

Application

Only one rule will be applied at a time. The first matching rule will be applied, in order from top to bottom. Thus "ReduceNow" and "ApproachNext" must be specified in the same rule if the aspect/from/to can potentially match a train performing these tests.

If a train is running to a timetable, and that timetable has a category assigned, and that category has caution speed set assigned, then that train will ignore sim-defined defensive driving techniques and instead use the ones supplied - even if none of the rules in the set match the current situation. Thus, a non-timetabled train (debug entry or "abandon timetable" has been used) will run to sim-defined defensive driving rules instead. Similarly, old timetables without defensive driving rules will also use sim-defined rules, i.e. carrying on as before with no changes required.

Because timetables are copied to trains when they enter, or are formed, any changes to rules after the train has entered (or been formed) will not apply to the active train. However, "run to timetable" will re-initialise the copied timetable and thus the rules.

Examples

"Our policy was reduce line speed by 33% at a double yellow, then reduce by 66% at the single yellow with a maximum of 15mph at the magnet or 200 yards before, depending which came first."

(Rule 1)

AspectPassed: YY
FromLineSpeed: 0
ToLineSpeed: 0
ReduceNowValue: 66
ApproachNextValue: 0
ApproachNextDistance: 0
NowValueType: Percent
NextValueType: Not applicable

(Rule 2)

AspectPassed: Y
FromLineSpeed: 0
ToLineSpeed: 0
ReduceNowValue: 33
ApproachNextValue: 10
ApproachNextDistance: 183 [metres]
NowValueType: Percent
NextValueType: Absolute

Pass shunt signals at 15mph:

AspectPassed: S
FromLineSpeed: 0
ToLineSpeed: 0
ReduceNowValue: 15
ApproachNextValue: 0
ApproachNextDistance: 0
NowValueType: Absolute
NextValueType: Not applicable

Reduce speed to 50% if passing a yellow; not dropping below 20mph (unless linespeeds or other decisions cause train to slow):

AspectPassed: Y
FromLineSpeed: 40 (because 50% of 40 is 20, the minimum speed)
ToLineSpeed: 0
ReduceNowValue: 50
ApproachNextValue: 0
ApproachNextDistance: 0
NowValueType: Percent
NextValueType: Not applicable

Last edited by GeoffM on 15/09/2016 at 03:01