KEY ASPECTS OF NAVIGATION - Speed 11. Definition Speed Limit-is the database representation of the...
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Transcript of KEY ASPECTS OF NAVIGATION - Speed 11. Definition Speed Limit-is the database representation of the...
KEY ASPECTS OF NAVIGATION- Speed
1
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Definition
Speed Limit-is the database representation of the Maximum Speed at which one is legally allowed or advised to drive a particular type of vehicle on a particular section of road.
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Description
Maximum Speed Limit Type - a speed that is associated with a legally enforceable limit of speed on a particular road or section of roadway. These signs tend to be white in color and situated on signs along roadways.
Vertical Event - the term that will be used when referring to Speed Limit signs, both yellow and white.
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Description
Recommended Speed Limit Type - a speed that is associated with an advisable speed limit on a particular road, section of road, or related to a particular road condition (i.e. bump, dip, animal crossing, or curve(s)). These signs tend to be yellow in color and situated on signs along roadways, particularly FOW 5.
Undefined Speed Limit Type - applied when the speed limit value can not be field verified either from a vertical event or stated in a general municipality law. Always attributed to Michigan U-turns, Texas U-Turns, and Ramp Rungs. The Speed Limit Value will be ‘0’.
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Speed Limit Types
Maximum Speed
Recommended Speed
Undefined
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Undefined Situations
Common situations when maximum speed could be unclear or ambiguous– Inaccessible Roads in Pedestrian Zones– Pathway– Entrance to/from Car Park– Roundabout & Special Traffic Figures
• If all incoming roads have the same Speed Restrictions, then these maximum speeds shall be captured for the feature.
• If all speeds entering are different but a recommended speed is present for the feature, then collect the recommended speed.
• In all other cases ‘Undefined’ shall be captured, indicating it is unclear which maximum applies.
– Roads with Restricted Access– MUTs, Texas U-Turns, Ramp Rungs
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Undefined Situations
Apply the Speed Limit value of ‘0’ when attributing ‘Undefined’ Speed Type in the Speed Limit tab.
The segments making up Michigan U-turns and Texas U-Turns, and Ramp Rungs will always have a value of ‘0’ and ‘Undefined’ for Speed Type.
This is because these segments normally do not have a posted speed in reality. This does not include small slip roads and jug handles.
Slip Roads and jug handles often do not have a speed posted; therefore, these types of roads will take the speed from the road from which they began. We will see an example on the next slide.
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Undefined Situations
If a small Slip Road has a speed posted in reality (i.e. vertical event), the posted speed will trump this rule.
A basic example of FOW 9 attribution for speeds. Note that a small slip road (FOW 9) will take the speed of the road from which it originates, even if not specifically posted with a vertical event.
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Speed Type Combinations
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Allowable Speed Type Combinations
Recommended Speed can coincide with Maximum Speed.
– The Recommended Speed shall always be lower than the accompanying Maximum Speed.
– If in reality both the Recommended and Maximum Speeds are the same, then ignore the Recommended Vertical Event. We do not want to duplicate Speed Limit Values. The same goes for duplication of Speed Limit Values in school zones.
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Allowable Speed Type Combinations
School Zone Maximum Speed can coincide with Maximum Speed.
– The School Zone Maximum Speed shall always be lower than the accompanying Maximum Speed.
– If in reality both the School Zone Maximum Speed and Maximum Speed are the same, then ignore the School Zone Vertical Event. We do not want to duplicate Speed Limit Values. The same goes for duplication of Speed Limit Values in Recommended Speed Limit zones.
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Non-Allowable Speed Type Combinations
Undefined for PC and a Maximum Speed/Recommended for another vehicle can not occur together
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General Capturing Rules
For each segment attributed with a Speed Limit, every vehicle type and every time period must be accounted for.
If DTRF is in both directions, then all vehicle types and time periods must be represented on both sides of the segment.
IF DTRF is one way, then all vehicle types and time periods must be represented on the direction of travel side only.
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General Capturing Rules
Speed Limits shall be captured for all Road Segments in the correct direction of travel, for which a permanent Maximum Speed or Recommended Speed is legally established
Speed Limit always refers to legal restrictions which are permanent Posted speeds always trump general city limit speeds When no signpost indicates a Maximum or Recommended speed,
Speed Type ‘Undefined’ shall be captured
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Maintaining Speed Limit Attribution
If the segment has a Speed Limit attributed to it, verify it. If the segment had a Speed Limit attributed to it before you edited it,
it should have a Speed Limit attributed to it after you edited it. If the segment did not have a Speed Limit prior to editing, check if
the segment is within ‘Scope’ for Speed Limit capture.
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Vertical Event Attribution Rules
- The 10 meter rule- The 30 meter rule
- The 500 meter rule
Three rules to remember when applying Speed Limit values to segments :
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10 Meter Rule for Speed Attribution
If a vertical event occurs within 10m of an existing database node, the attribution will begin/end at the existing node.
If a vertical event occurs further than 10m of an existing database node, a new node must be created in the database, and the attribution will begin/end at the new node.– We want to make sure we use the 10m rule appropriately. We do not
want to overpopulate the data base with nodes if the existing nodes are within the 10m tolerance.
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30 Meter Rule for Speed Attribution
If a vertical event is detected within 30m of an intersection, the speed for that vertical event is backwards attributed to the intersection.
If the vertical event is more than 30m from an intersection, the vertical event is not backward attributed to the intersection; rather a previous vertical event is attributed through the intersection up to the next vertical event.
backwards attributed, <30 M
Previous vertical event carried through intersection, >30 M
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500 Meter Rule for Speed Attribution
At the beginning of a street, the first Vertical Event after the intersection less than 500 meters will be considered valid for the segments backward to the intersection.
In the case that no Vertical Event can be found within 500m of the beginning of any local road, apply ‘Undefined’ until the next vertical event.
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500 Meter Rule for Speed Attribution
DTRF DTRF
< 500
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Vertical Event Attribution Stops When…
the road ends or, when a Vertical Event of a different value is encountered. When
this happens, the value of the new Vertical Event will be collected from the nearest node if within 10m or a new node will be added at the spot of the vertical event.
It is important to understand the concept that Vertical Event attribution happens from point……..
A B CVertical Event
Vertical Event
Vertical Event
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Validity Periods
A Speed Limit value can be restricted by a Validity Period. Usually, restrictions are applied on Maximum Speeds, however, Recommended Speeds can be restricted as well.
For any Validity Period, the minimum capture distance is 10m. However, it should be noted that it is quite often that Validity Period distances far exceed this distance.
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Validity Periods
Speeds will be captured from the Vertical Event (or a node nearby if within 10m) where the validity period begins in reality.
SL attribution for Validity Period ends at the Vertical Event indicating the end of a Validity Period “zone” or when a reasonable distance has occurred and it is obvious that the Validity Period “zone” ended (or a node nearby if within 10m).
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Validity Period Specifications
Where there are School Speed Limits, there is often a regular Maximum Speed Limit present as well as a School ‘Maximum’ Speed Limit (valid during certain times on School Days)
The regular Maximum Speed Limit should be collected throughout. And the school-related Maximum Speed Limit may also be collected
for the pertinent segments and day/times is allowed to overlap the segments carrying the normal Maximum Speed Limit.
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Validity Period for School Zone
For school zones, apply normal Maximum Speed Limits on the whole segment. If nodes are dropped to apply speed limits at a school zone, leave the normal Maximum Speed, 24/7, on the school zone section in addition to the specific school zone speed and time domain.
Add applicable time domain information and VTRs (Vehicle Type Restrictions).
If no specific time domain is stated, use the “fuzzy time” domain of “School Days” for VTRs related to the Maximum Speed Limit for the validity school zone segments.
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Recommended Speed Limit Situations
Curved Situations
Recommended Speed Limits related to curves.
It will be necessary to attribute the curve speed only to the curved portion of the road.
Both Maximum and Recommended Speed Types will need to be applied to the segments making up the curved portion.
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Recommended Speed Limit Situations
Some intersections may be posted with a Recommended Speed for safety as in the case of intersections with a limited sight hazard.
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Recommended Speed Limit Situations
Placement concerning the beginning of the Recommended Speed zone for intersections, such as limited sight, is at the discretion of the editor, however, the following variables should be kept in mind.
– If the Recommended Vertical Event occurs well before the limited sight zone, begin the Recommended Speed zone closer to the intersection, near the bottom of the hill approaching the intersection.
– If the Vertical Event occurs near the bottom of the hill, begin your Recommended Zone at the location of the Vertical Event.
– The Recommended Speed zone must be at least 10 meters.
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Recommended Speed Limit Situations
The Recommended Speed zone ends at the intersection for which the Vertical Event was intended for.
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Local Road Intersection Scenarios
The following examples are designed to visually describe how specific intersections should be handled during field attribution of speed restrictions. This information is based upon a variety of sources, and should be considered the most valid (visual) available for current surface road speeds. Not every intersection will be described.
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Local Road Intersection Scenarios
“Nodes” in the following figures indicate multi-valence nodes, and are used only to clarify specific connections. These are NOT indicative of grade separations.
Speed attribution is assumed to continue beyond the schema indicated. These figures are to be seen as “close-ups” of specific intersections in the database.
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Single Carriage Attribution
55MPH max speed sign occurs less than 30m from the intersection, the speed is “pulled back” so that the speed change is applied at the actual intersection.
DTRF
Sign A Sign B
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Single Carriage Attribution
The 55MPH max speed sign occurs greater than 30m from the intersection. The speed change is applied at the vertical event.
DTRF
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Intersections – Single Carriage
On left, application of the 30m rule (in this case greater than 30m) On right, application of slip road Fow 9 speeds (even though there is no posted sign for the FOW 9, the speed value and type is equivalent to the street [FOW 9] begins from)
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Intersections – Single Carriage
On left, application of the 30m rule (in this case less than 30m) On right, application of slip road FOW 9 speeds (even though there is no posted sign for the FOW 9, the speed value and type is equivalent to the street [FOW 9] begins from)
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Intersections – Single Carriage
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Dual Carriage Intersections
Dual carriage attribution of speeds at intersections can be tricky. This is due to the fact that, when a speed changes after progression though an intersection, segments internal to a dual-carriage intersection must be attributed properly. This usually means that:
- The 30 Meter rule should be checked first.- If the next vertical event is less than 30m from the intersection, the most restrictive (i.e. lowest) value must be placed on internal segments for any given direction on a dual carriage.
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Dual-Carriage Intersections
The application of the 30m rule (in this case both situations are shown, one greater than 30m, one less than 30m)
Be careful; in situations like this, the lower of two competing values must be attributed internal to an intersection.
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Dual-Carriage Intersections
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Roundabouts (FOW 4)
The figure at right has different incoming speeds. Therefore, the Speed Type for the FOW 4 is captured as ‘Undefined’; this indicates that it is unclear which maximum speed applies.
The figure at left has equal value incoming speeds from all directions. Therefore, the roundabout is captured with the maximum speed of the incoming roads.
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Roundabouts (FOW 4)
This Traffic Circle has a recommended speed posted for the roundabout (35 MPH). Therefore, the roundabout is captured with the posted recommended speed. Since all incoming speeds are identical, the maximum speed of 45 MPH is also applied to the roundabout.
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Roundabouts (FOW 4)
In this example, all incoming and outgoing roads have different Speed Limits, so no Maximum Speed can be attributed to the FOW 4. However, a Recommended Speed is posted for the FOW 4 and will be
the only Speed Type attributed for this feature.
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Dual Carriage to Single Carriage
The application of the 30m rule (in this case both situations are shown, one greater than 30m, one less than 30m).
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Beginning of Street Examples
At the beginning of a street, the first Vertical Event after the intersection less than 500 meters will be considered valid for the part of the segment(s), even if the distance is greater than 30m. This is unique for each driving direction, and is considered a valid exception to the 30m rule as explained If no Vertical Event can been found greater than 500 meters, then the Speed Type Undefined will be attributed to all segments from the intersection until a speed can be verified on a vertical event or as stated by municipal written law.
45
< 500
Undefined
> 500
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Curved Intersections
The recommended speed present for the “S” curve must be attributed though the intersection, until the series of curves is complete.
The best guidance for when a curve is complete is when you feel that the “driver” of an auto mobile would have the steering wheel pointed straight ahead, in combination with the visual evidence gathered from the geometrical depiction shown on the sign (vertical event). This can be a relatively subjective decision during attribution.
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Exercise
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Speed Limit 50 MPH
Would you collect this Vertical Event?
Yes
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Work Zone Speed Limit 55
Would you collect this Vertical Event?
No, Why? Not a permanent sign Carry the previously
observed value through this construction zone if you can not verify the normal posted speed
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Slow School
Would you collect this Vertical Event?
No Why? No Speed Limit Value
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How Does The Speed Info Get Applied To The Curve?
Where does the speed information get applied?
Both Maximum and Recommended will be applied to the curve portions of the road, within 10 meters of an existing node at the beginning and ending of the curved geometry
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Do Speed Limits Have Validity Periods?
Can validity be applied to a speed limit?
Absolutely VTR for this Vertical Event =
All vehicles on School Days School zone must be at least
10 meters long
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FAQs
Following are some of the frequently asked Questions :
Q: If no Speed Limit is posted on a Vertical Event in a school zone, however it is locally known and stated in municipal documentation that certain speeds are to be applied in this situation. Can we apply the municipal speed limits if we verify the law with out visually seeing a Vertical Event with a speed value?
A: Yes. The municipal law must be verified before we can attribute SL info for situations like this. Remember, posted values on all permanent Vertical Events will trump general city speed limit signs and general municipality speed laws not seen in reality. Generally, Speed Restrictions can be derived from traffic signs or -if no signs are present- from general traffic rules. Thank you for your question.
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FAQs
Q: In some validity period situations, exact times may not be represented on the Vertical Event, but rather flashing lights will indicate the times at which to obey the posted speed limit. How can we represent this?
A: If the GFA can not confirm a validity period time either from local knowledge or information posted on a vertical event, then GFA must contact authorities or school administration offices and confirm the times for which these flashing lights will be valid? If this is not possible, then use the fuzzy time domain ‘School Days’.
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FAQs
Q: Inside slip roads/turn channels-What speed value is attributed to inside FOW 9 slip roads/turn channels?
A: Inside slip roads and turn channels that have a FOW value of 9, will follow the same rules as a right hand slip road. Therefore, the inside FOW 9 will be attributed with the same speed value as the road from which it began, unless, a permanent Vertical Event posted on the FOW 9 states otherwise.
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FAQs
Q: I know FOW 5 on ramps are attributed as ‘Undefined’ unless otherwise posted, FOW 9 small slip roads take the SL value from the road it began from unless otherwise posted, but what is the rule for FOW 18?
A: Treat them as part of the FOW 5 complex. In other words, don't consider them as FOW 9. they will receive the Speed Type of ‘Undefined’ unless otherwise posted.
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Questions
