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VS-GPS
GPS-Based Trip Evaluation
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Introduction |
VS-GPS is a GPS-based trip evaluation system. Using a
commercially available PDA (Personal Digital Assistant)
together with a GPS unit and custom software, it collects
vehicle position data once per second and provides a wide
range of detailed analysis. It can be used both for public
transport and for individual traffic data collection and
evaluation.
The mobile equipment records the position data of a vehicle
each second. Additional user-input information such as
waypoints and relevant traffic points can be stored by pushing
pre-defined keys.
After recording, the data undergoes error correction to fix
inaccuracies of the GPS protocol and the measuring
method.
The collected data, once imported into the VS-GPS Analyzer can
be shown in diagrams and tables. It is also possible to
compare several trips by diagrams and tables.
The end result is a highly valuable use set of analytics,
which include:
Before and After Studies. Whether for pre-defined routes or
preset begin and endpoints, for traffic flows or public
transportation, the ability to compare in great detail, both
graphically and statistically can clearly illustrate the
actual results of specific changes, or track long-term
changes.
Measuring Time Loss. The evaluations can identify
specifically (where and when) time is lost. This can be for
public transportation, either in route sections or at
intersections, or it can be for individual traffic flows.
Identifying Actual Level of Priority. By comparing
different traffic flows (public, private, emergency) by
location and time, the actual level of priority can be clearly
identified.
Measurement of Variances. By comparing measurements,
the actual level of variability in traffic flows (either
individual or public transport) can be clearly identified.
Association of Probable Causes. By using the
user-defined inputs, probable causes of time loss or variance
can be identified.
Traffic Control Coordination Evaluation. Actual traffic
coordination effectiveness can be measured. By using the user
defined inputs, various associations can be included.
Traffic Engineering Statistics. The various data and
analysis tools provide a rich world of traffic engineering
statistics that can be used for both spot evaluations and,
importantly, long-term evaluations.
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VS-GPS
Collector |
The VS-GPS Collector is the "front-end" of the
VS-GPS system. The Collector consists of a commercial PDA, a
GPS plug-in chipset and antenna unit, and the VS-GPS PDA
collector soft-ware. The collector on the PDA records GPS
position data in a compressed binary file format. User defined
data is saved in the same file.
After recording, the data is transferred from the PDA to a
Windows computer.
Recording on a portable computer is also possible.
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VS-GPS
Analyzer |
The VS-GPS Analyzer is a software package designed
specifically to supply a wide range of high value traffic and
travel data analysis. The binary files, as supplied by the
mobile unit, are read by the Analyzer and converted into
Cartesian coordinates for use in evaluations, statistics and
pro-files.. Additionally, ASCII files can be imported,
following the NMEA 0183 standard, which are provided by all
commercially available GPS receivers.
A variety of data cleaning functions are avail-able.
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Geographical
Representation |
Each trip is shown in two dimensions. Different measurements
have different colors. A map bit-map can be selected as
background picture.
It is also possible, to select the color according to the
speed, which results in a good insight into the vehicle
trajectory. This is possible in all geo-graphical
representations and evaluations.
In the geographical representation, further information can be
shown or added to the data, like names of intersections or bus
stops. Such information can also be copied into the actual
measurements basing on earlier measurements having been
exported into a reference point file.
The measurements can be cleaned from incorrect data. The
measurements can be divided into sections, either on a
straight trip or between the terminals of a public transport
vehicle.
It is, for example, possible to cut a bus log file into parts
between the two last stops, re-arrange the parts and evaluate
bus data always driving in the same direction. Likewise, it is
possible to cut vehicle trips into user defined sections for
various levels of comparison and analysis
The same flexibility can also be applied to all of the
specific evaluation diagrams described be-low.
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Time
Space Diagram |
This diagram shows the driven distance in relation to the time needed.
The Time-Space diagram is well suited for displaying several
trips together and showing how some of the trips were faster
and some were slower.
In the example, one sees that the two trips are very much
alike for the first 1400 meters. Then however, the green trip
gets stuck for more than 4 minutes in a queue before an
intersection, while the red trip is stopped only a few
seconds. At the second crossing, the red trip does not stop at
all, while the green trip must wait again two more minutes.
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Distance
Speed Diagram |
In the next graph, the parts of the trip between the stops can
be seen nicely, as well as the driven speed.
This diagram is optimal for comparing several measurements
among themselves, since the distance of all trips is constant
and therefore pro-vides a good reference for comparison.
In the example, one can see at distance 1400m, that the green
trip had to stop in front of a traffic light about 100 meters
earlier than the red trip. At distance 2200m, the green trip
had even to wait for two traffic light cycles before
continuing. Red again was lucky and did not have to stop.
All measurements and analysis can be shown in metric units or
in feet, miles and miles per hour.
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Time
Speed Diagram |
The Time-Speed diagram shows the driven speed in relation of
the necessary travel time. Various traffic conditions, such as
the waiting time before traffic lights or in traffic back-ups
among others can be seen very clearly in the diagram and are
clearly associated with both time and location.
In the example, one sees the red trip recorded in a low
traffic period. The green trip however was recorded at the
peak hour on Friday afternoon. It can be seen very well that
the green trip loses a lot of time at two signaled
intersections. The red trip was able to almost drive without
stops for the whole trip.
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Statistics |
Statistical functions combine several measurements. If only one single
measurement is pre-sent, they cut this measurement in segments between reference
points and name them ac-cording each destination reference point.
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Distance |
The evaluation of the distances guarantees that all trips are comparable due to
their equivalent lengths. The evaluation method can also be interesting if a
trip is only defined by the starting and the terminating point and the route
choice in-between is free.
For each trip a bar is shown. Additionally the average distance is shown as a
horizontal line.
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Speed |
The speed statistics calculates the mean speed for each measurement or for each
segment in case of only 1 measurement.
Detail speed information of each trip can be seen from the trip profile, which
is described later.
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Number
of Stops |
The stops statistics calculates the number of stops for each measurement or for
each segment in case of only 1 measurement. A stop is reached when the speed
falls under a certain defined level.
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Travel
Time |
The travel time statistics calculates the total time needed for each measurement
or for each segment in case of only 1 measurement.
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Distribution
Functions |
All graphics panels can be shown in a distribution function view, e.g. a speed
distribution of a speed statistics diagram:
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Numeric
Values |
The numeric values of everything shown on the graphics panels and of the
distribution panel can be copied or exported to other programs.
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Profiles |
Profiles are statistical diagrams as well, however they go
much more into the details for each trip. Profiles are
normally used for a group of trips along with a reference
trip. They can be used for single trips as well. Profile
evaluations break down the driven distance into discrete
intervals and evaluate duration or speed per interval.
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Speed
of a Single Trip |
Reference points can be defined for a single trip. The reference points can be
recorded either during the measuring trip by pressing keys, or they can be
inserted later into one of the evaluations. An average speed can be calculated
between such reference points.
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Speed
of Several Trips |
The same evaluation applies for a group of trips. Additionally a mean speed per
section can be calculated.
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Speed
Differences |
Any trip can be defined as being the reference trip. In this example we choose
the measurement called "third trip". Now we can calculate the
difference to the reference speed of each trajectory.
In order to do so, the entire distance is divided in equally long, short
intervals (here of a length of 20 m), and in all of these short intervals the
average speed of the reference trip and the other trips is computed.
Additionally, the computed values can be aver-aged between the reference points
and shown in a graph or a table. This leads to a stepwise constant function that
is constant within a section between two reference points.
The next figure shows the distribution function of the speed differences to the
reference trip.
The number of observations equals the number of sections of 20 m length, in
which the corresponding speed difference was observed. The speed difference is
here mapped into intervals of 5 km/h.
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Delay
Times |
Instead of speed, delay time can be calculated. In order to be able to compare
the individual sections between reference points among each other, the delay
time has to be mapped to the small intervals as well (here of 20 m
length).
The delay times are inverse proportional to the speed differences.
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Travel
Times |
Finally travel time can be calculated without the link to a reference trip. The
absolute travel time is, again, calculated per small interval (of 20 m).
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Contact |
Please use the contact
form if you wish to receive more information about VS-GPS of a demo version.
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