5. Implementation of Weather-Related Features in DYNASMART
This section entails a description of newly added weather related options and associated input files in DYNASMART. The overview of those weather related features is provided in Table 5-1. First, weather conditions can be specified by users for either an entire network or an individual link through "weather.dat". Traffic performance is then simulated in DYNASMART based on the adjusted supply-side parameter relations that are provided through a user-specified input file, "WAF.dat". In addition to the simulation of the weather effect on traffic performance, users can also simulate traffic advisory and control strategies by using various VMS options. Along with existing four types of VMS in DYNASMART, another three weather-related VMS options are developed and implemented, namely, speed reduction VMS, travel risk warning, and variable speed limits. Aside from these new VMSs, an existing mandatory detour VMS could also used to inform drivers of extreme weather conditions and mandate all vehicles to detour, when a certain area or road is closed due to safety concerns as discussed in the previous section. The detailed descriptions of data preparation for these features are presented in the remainder of this section.
| Weather-related option | Description | Associated input file |
|---|---|---|
| Weather data representation | Specify various weather scenarios for the study network over time. Allow users to specify either network-wide weather condition or link-specific weather condition. |
weather.dat |
| Applying the weather effect to supply-side parameters | Specify change in supply-side relation and operational parameters regarding weather conditions by applying a weather adjustment factor(WAF) | WAF.dat |
| Modeling traffic advisory (speed reduction) via VMS | Simulate the effect of speed reduction advisory through VMS | vms.dat |
| Modeling traffic advisory (travel risk warning) via VMS | Simulate user response to travel time delay information provided by VMS under inclement weather condition | vms.dat |
| Modeling traffic control (Variable Speed Limits) via VMS | Simulate the effect of variable speed limit control through VMS | vms.dat, vsl.dat, weather.dat |
5.1 Weather Data (weather.dat)
For the weather scenario, three link-specific weather parameters can be specified by users, that is, visibility, rain intensity and snow intensity. The default values of these parameters correspond to clear weather conditions, that is, no precipitation and visibility greater than 10 miles. Based on the regional weather conditions, the user could modify all or some of the weather parameters (v, r, s) of the links within the impacted area. A new input file, namely weather.dat, is created to store the adverse weather specifications, described in Table 5-2.
| Record Type | Field | Format | Width | Description |
|---|---|---|---|---|
| Network-wide Weather flag |
1 | Integer | Free | 1: A network-wide weather condition exists; 0: otherwise |
| Network Weather Information | 1 | Float | Free | Visibility (mile). |
| Network Weather Information | 2 | Float | Free | Rain intensity (inch per hour) |
| Network Weather Information | 3 | Float | Free | Snow intensity (inch per hour) |
| Network Weather Information | 4 | Float | Free | Start time of the across-the-board weather condition (minutes) |
| Network Weather Information | 5 | Float | Free | End time for the across-the-board weather condition (minutes) |
| Number of links | 1 | Integer | Free | Number of links with link-specific weather condition |
| Link Information | 1 | Integer | Free | Link counter (1st link with inclement weather condition) |
| Link Information | 2 | Integer | Free | From node |
| Link Information | 3 | Integer | Free | To node |
| Link Information | 4 | Integer | Free | Number of time periods |
| Weather Information | 1 | Float | Free | Start time for the 1st weather condition (minutes) |
| Weather Information | 2 | Float | Free | End time for the 1st weather condition (minutes) |
| Weather Information | 3 | Float | Free | Visibility (mile) |
| Weather Information | 4 | Float | Free | Rain intensity (inch per hour) |
| Weather Information | 5 | Float | Free | Snow intensity (inch per hour) |
 |
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| Weather Information | 1 | Float | Free | Start time for the Nth weather condition (minutes) |
| Weather Information | 2 | Float | Free | End time for the Nth weather condition (minutes) |
| Weather Information | 3 | Float | Free | Visibility (mile) |
| Weather Information | 4 | Float | Free | Rain intensity (inch per hour) |
| Weather Information | 5 | Float | Free | Snow intensity (inch per hour) |
|
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| Link Information | 1 | Integer | Free | Link counter (last link with inclement weather condition) |
| Link Information | 2 | Integer | Free | From node |
| Link Information | 3 | Integer | Free | To node |
| Link Information | 4 | Integer | Free | Number of time periods |
| Weather Information | 1 | Float | Free | Start time for the 1st weather condition (minutes) |
| Weather Information | 2 | Float | Free | End time for the 1st weather condition (minutes) |
| Weather Information | 3 | Float | Free | Visibility (mile) |
| Weather Information | 4 | Float | Free | Rain intensity (inch per hour) |
| Weather Information | 5 | Float | Free | Snow intensity (inch per hour) |
|
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| Weather Information | 1 | Float | Free | Start time for the Nth weather condition (minutes) |
| Weather Information | 2 | Float | Free | End time for the Nth weather condition (minutes) |
| Weather Information | 3 | Float | Free | Visibility (mile) |
| Weather Information | 4 | Float | Free | Rain intensity (inch per hour) |
| Weather Information | 5 | Float | Free | Snow intensity (inch per hour) |
If both across-the-board network weather condition and link-specific weather condition are defined, link-specific weather information dominates, namely, link-specific weather information applies regardless of the network weather condition; while network weather condition applies for all the links without the link-specific weather condition.
An example weather.dat file is shown in Figure 5-1. Particularly, a network-wide weather condition is specified on the first line, namely, low visibility of 0.5 mile and rainfall at the rate of 0.1 inch/hour during the first 2 hours (0 to 120 minutes). In addition, three (i.e. the number on the second line) link-specific weather conditions are defined in the rest of the file. The first link is from node 4042 to 4087 and has two weather events: during 10-40 minutes, the visibility is 1.0 mile with rainfall intensity of 0.1 inch/hour; and during 41-60 minutes, the visibility decreased to 0.5 mile and rainfall intensity increased to 0.2 inch/hour. The second (on the link of 4084 to 4042) and the third (on the link of 3826 to 581) link-specific weather events are defined in the same fashion.
Figure 5-1. General Format of the weather.dat input file
Once the weather input file is created, the DYNASMART-P program will return to estimate and predict traffic conditions through the procedure designed to incorporate traffic impact by inclement weather condition. This procedure requires additional components for the entire system to support the efficient and reliable estimation and prediction of traffic impact due to weather changes, discussed next.
5.2 Weather Adjustment Factor Data (WAF.dat)
When DYNASMART-P receives inclement weather input, a model is needed to simulate traffic conditions affected by inclement weather within DYNASMART-P. For example, an adjustment factor for capacity, free-flow speed, and saturation flow can be applied in the simulator, which is obtained based on the inclement weather parameters (visibility, rain intensity and snow intensity) and the calibrated weather-traffic flow relation. This section describes the impact of weather on the relationships between traffic speed, flow, and density, and other macroscopic measurements.
Both the functional form and the parameter values (free mean speed, jam density, breakpoints for multiple regime models) may be affected by weather, and may be affected differently by the characteristics of different weather instances. The FHWA (2006) report by Cambridge Systematics summarizes changes in the so-called fundamental diagram observed at a limited number of locations (e.g. Twin Cities, Minnesota, shown below). These results suggest a relatively simple-to-apply modification to the existing model underlying traffic propagation on freeways in DYNASMART-P (and -X). Although the applicability of this modification to other environments, or to more extreme conditions in the same environment is not evident, it provides a good starting point for the modification to be implemented. Parameters that are relevant to inclement weather impacts in the supply side of DYNASMART-P are listed by the type of input data in the following table.
| Input data | Traffic properties | Note |
|---|---|---|
| Traffic flow model | 1. Speed-intercept , (mph) 2. Minimal speed , (mph) 3. Density break point , (pcpmpl) 4. Jam density , (pcpmpl) 5. Shape term alpha |
The italic styled properties are only available in dual-regime model |
| Link | 6. Maximum service flow rate, (pcphpl or vphpl) 7. Saturation flow rate , (vphpl) 8. Posted speed limit adjustment margin, (mph) |
|
| Signal control | Cycle length, offset, green, amber, max green, min green | All same units, (seconds) |
| Left-turn capacity | 9. g/c ratio | |
| 2-way stop sign capacity | 10. Saturation flow rate for left-turn vehicles 11. Saturation flow rate for through vehicles 12. Saturation flow rate for right-turn vehicles |
All same units, (vphpl) |
| 4-way stop sign capacity | 13. Discharge rate for left-turn vehicles 14. Discharge rate for through vehicles 15. Discharge rate for right-turn vehicles |
All same units, (vphpl) |
| Yield sign capacity | 16. Saturation flow rate for left-turn vehicles 17. Saturation flow rate for through vehicles 18. Saturation flow rate for right-turn vehicles |
All same units, (vphpl) |
The inclement weather impact on each parameter listed in Table 5-3 can be represented by a corresponding weather adjustment factor (WAF).
where
Fi = weather adjustment factor for parameter i
v = visibility
r = precipitation intensity of rain
s = precipitation intensity of snow
β0, β1, β2, β3, β4, β5 = coefficients
the new input file, namely WAF.dat, is created to store the specifications of above mentioned coefficients, described in Table 5-4.
| Record Type | Field | Format | Width | Description |
|---|---|---|---|---|
| Weather Adjustment Factor | 1 | Integer | Free | Parameter index (as shown in Table 2) |
| Weather Adjustment Factor | 2 | Float | Free | Constant term for 1st parameter |
| Weather Adjustment Factor | 3 | Float | Free | Coefficient of visibility term for 1st parameter |
| Weather Adjustment Factor | 4 | Float | Free | Coefficient of rain intensity term for 1st parameter |
| Weather Adjustment Factor | 5 | Float | Free | Coefficient of snow intensity term for 1st parameter |
| Weather Adjustment Factor | 6 | Float | Free | Coefficient of interaction term of visibility and rain intensity for 1st parameter |
| Weather Adjustment Factor | 7 | Float | Free | Coefficient of interaction term of visibility and snow intensity for 1st parameter |
|
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| Weather Adjustment Factor | 1 | Integer | Free | Parameter index (as shown in Table 2) |
| Weather Adjustment Factor | 2 | Float | Free | Constant term for the last parameter |
| Weather Adjustment Factor | 3 | Float | Free | Coefficient of visibility term for the last parameter |
| Weather Adjustment Factor | 4 | Float | Free | Coefficient of rain intensity term for the last parameter |
| Weather Adjustment Factor | 5 | Float | Free | Coefficient of snow intensity term for the last parameter |
| Weather Adjustment Factor | 6 | Float | Free | Coefficient of interaction term of visibility and rain intensity for the last parameter |
| Weather Adjustment Factor | 7 | Float | Free | Coefficient of interaction term of visibility and snow intensity for the last parameter |
An example WAF.dat file is shown in Figure 5-2. The first line corresponds
to the Speed-intercept parameter listed in Table 5-3. The constant term in Equation
(5-1) is 0.91 for this parameter; and the coefficients for visibility, rain
and snow precipitation are 0.009, -0.404 and -1.455 respectively. Thus the weather
adjustment factor for Speed-intercept can be calculated as follows.
The rest of file specifies coefficients for the other 17 parameters listed in Table 5-3.
DYNASMART-P provides the capability of allowing multiple signal timing plans, each of which corresponds to a certain time period (defined by a start time and an end time). Therefore, these times and associated signal controls could be defined to correspond to the weather event(s) of interest.
Figure 5-2 General Format of the WAF.dat Input File
5.3 Variable Message Signs (vms.dat)
As three types of new VMS are introduced, currently seven types of VMS are supported by DYNASMART-P. Type 1 VMS is the speed advisory VMS that allows users to increase/decrease speed by a certain percentage below/above a certain threshold. Type 2 VMS is the mandatory detour VMS that advises drivers of lane closures, and mandates all vehicles to follow some user-specified sub-path in the vicinity. Type 3 VMS is the congestion warning VMS, which allows users to specify percentages of VMS-responsive vehicles (user class 5) to evaluate the VMS information and divert if a better path exists. Therefore, the user is advised to select VMS type 3 on links that would provide diversion points. Type 4 VMS is the optional detour VMS. Similar to type 2, it also advises drivers with lane closure information. However, type 4 gives drivers the option to follow the detour path or keep their original path, based on the boundedly rational decision rule. Type 5 VMS is the speed reduction (weather) VMS, which suggests a speed reduction due to adverse weather conditions. Type 6 VMS is the travel risk (weather) VMS, which suggests all VMS-responsive and en-route info vehicles to reevaluate their current route and divert to a better route, if exists, considering the weather-related travel penalty associated with the link. Type 7 VMS is the variable speed limits (weather) VMS, which adjusts speed limits according to the weather condition and a look-up table (defined in a separate file vsl.dat). The vsl.dat file allows users to specify multiple variable speed limits (VSL) look-up tables, each of which could define different weather conditions and the corresponding speed limits. Detailed description of this file and its format are provided in Table 5-5 and Figure 5-3, respectively.
| Record Type | Field | Format | Width | Description |
|---|---|---|---|---|
| Number of signs | 1 | Integer | Free | Number of Variable Message Signs |
| Sign description | 1 | Integer | Free | Type of VMS according to the following description 1: speed advisory; 2: mandatory detour; 3: congestion warning; 4: optional detour; 5: speed reduction (weather); 6: travel risk; 7: variable speed limits |
| Sign description | 2 | Integer | Free | Upstream node of the 1st VMS link |
| Sign description | 3 | Integer | Free | Downstream node of the 1st VMS link |
| Sign description | 4 | Integer | Free | Type 1: speed threshold (+ or -) (mph)1 Type 2: 1002 Type 3: percentage of user class 53 who will actually evaluate and respond to the VMS information Type 4: 1002 Type 5: 1002 Type 6: value of risk (default value is 1) Type 7: 1002 |
| Sign description | 5 | Integer | Free | Type 1: percentage reduction or increase in VMS link speed Type 2: number of nodes in detour sub-path Type 3: path preference (0 or 1) for diversion 1: current best path; 0: a random path among K-paths Type 4: number of nodes in detour sub-path Type 5: speed reduction on the VMS link Type 6: travel penalty (percentage of link travel time) Type 7: look-up table number |
| Sign description | 6 | Float | Free | Start time for the 1st VMS (minutes) |
| Sign description | 7 | Float | Free | End time for the 1st VMS (minutes) |
| Subpath4 | 1 | Float | Free | 1st node in the detour sequence for the 1st VMS (if applicable) |
| Subpath4 | N | |
|
Last node in the detour sequence for the 1st VMS (if applicable) |
| Sign description | 1 | Integer | Free | Type of VMS according to the following description 1: speed advisory; 2: mandatory detour; 3: congestion warning; 4: optional detour; 5: speed reduction (weather); 6: travel risk; 7: variable speed limit |
| Sign description | 2 | Integer | Free | Upstream node of the last VMS link |
| Sign description | 3 | Integer | Free | Downstream node of the last VMS link |
| Sign description | 4 | Integer | Free | Type 1: speed threshold (+ or -) (mph)1 Type 2: 1002 Type 3: percentage of user class 53 who will actually evaluate and respond to the VMS information Type 4: 1002 Type 5: 1002 Type 6: value of risk (default value is 1) Type 7: 1002 |
| Sign description | 5 | Integer | Free | Type 1: percentage reduction or increase in VMS link speed Type 2: number of nodes in detour sub-path Type 3: path preference (0 or 1) for diversion 1: current best path; 0: a random path among K-paths Type 4: number of nodes in detour sub-path Type 5: speed reduction in the VMS link Type 6: travel penalty (percentage of link travel time) Type 7: look-up table number |
| Sign description | 6 | Float | Free | Start time for the last VMS (minutes) |
| Sign description | 7 | Float | Free | End time for the last VMS (minutes) |
| Subpath4 | 1 | Float | Free | 1st node in the detour sequence for the last VMS |
| Subpath4 | N | |
|
Last node in the detour sequence for the last VMS |
| 1 If positive (+), link speed will be increased (if link
speed is lower than the threshold). If negative (-), link speed will be
decreased (if actual link speed is higher than the threshold). 2 This entry is read but ignored by DYNASMART-P. It is used to keep the same number of fields for VMS types. 3 If the VMS preemption mode is set to 1 (in scenario.dat), then this fraction applies to user classes 2-5. 4 For VMS types 2, 4 only. |
||||
An example vms.dat is shown in Figure 5-3. The first record indicates that there are 7 VMS locations or sites. The second record states that a type 1 (speed advisory) VMS (field 1) is located between upstream node 1 (field 2) and downstream node 20 (field 3). A +40 mph threshold is given (field 4). The positive sign indicates that if the link speed is less than 40 mph, VMS-responsive vehicles will attempt to increase their speed to reach this speed. If their speed is already above 40 mph, then no action is taken. The next field indicates that VMS responsive vehicles (user class 5) will increase their speed by 10 percent to achieve the recommended speed threshold. The VMS is activated from time 10.0 (field 6) until time 30.0 minutes (field 7).
The third record (2nd VMS link in network) shows that there is a detour type VMS (type 2) (field 2) located between upstream node 53 and downstream node 52. All vehicles need to divert (100%) and there are three nodes in the specified sub-path for detouring. This VMS is activated between minutes 10.0 (field 6) and 80.0 (field 7) of simulation. The next immediate record specifies the node sequence of the sub-path for detouring. The first node is 52, which is required to be the downstream node of the VMS (there is no requirement for the last node on detour sub-path); the remaining two nodes on sub-path are 51 and 14. The mandatory detour-type VMS is of particular importance for work zone and incident operational management strategies, and extreme weather events.
The fourth record (3rd VMS link in network) shows that there is a congestion warning VMS (type 3) (field 1) located between upstream node 48 (field 2) and downstream node 41 (field 3), and a response rate of 15 percent (field 4) is specified. After diversion, vehicles will be assigned the current best (1) path (field 5) starting from the downstream node of the VMS link. The VMS will be activated from minute 0.0 (field 6) until minute 20.0 (field 7).
The fifth record (4th VMS link in network) shows that there is a weather advisory VMS (type 5) (field 1) located between upstream node 53 (field 2) and downstream node 52 (field 3). The VMS suggests a speed reduction (field 4) due to adverse weather conditions. In particular, 5 mph reduction (field 5) in speed is specified for the vehicles traveling on the link during minute 0.0 (field 6) until minute 20.0 (field 7).
The sixth record (5th VMS link in network) shows that there is a weather advisory VMS (type 6) (field 1) located between upstream node 53 (field 2) and downstream node 52 (field 3). The VMS suggests all VMS-responsive vehicles to reevaluate their currents route and divert to a better route, if exists, considering the travel risk associated with the link (field 4 indicates the value of risk). A weather-related travel penalty, 10% extra travel time (field 5) is included in the generalized cost. This VMS is activated between minutes 20.0 (field 6) and 40.0 of simulation (field 7).
The seventh record (6th VMS link in network) shows that there is a weather-responsive variable speed limits (type 7) (field 1) located between upstream node 48 (field 2) and downstream node 41 (field 3). The speed limits are determined based on look-up table 1 (field 5) in vsl.dat. This VSL is activated between minutes 10.0 (field 6) and 20.0 of simulation (field 7).
Figure 5-3. General Format of the vms.dat Input File
5.4 Variable Speed Limits via VMS (vsl.dat)
In order to implement type 7 VMS (Variable Speed Limits) in DYNASMART, an additional file vsl.dat needs to be prepared to specify speed limit regulation through one or more look-up tables. In each look-up table, one or more weather conditions are specified, as well as the corresponding speed limit reductions. For example, if there are links whose posted speed limit is 65 mph and variable speed limits under rain and snow are 55 mph and 45 mph respectively, the look-up table has two lines that state the speed reduction of 10 mph (65-55mph) for rain and 20 mph (65-45 mph) for snow. The posted speed limit for all the links in the network is specified in a separate input file (network.dat) and these values are used when calculating actual speed limit for certain links in DYNASMART.
| Record Type | Field | Format | Width | Description |
|---|---|---|---|---|
| Number of tables | 1 | Integer | Free | Number of look-up tables for VSL |
| Table description | 1 | Integer | Free | Look-up table counter |
| Table description | 2 | Integer | Free | Number of lines in the table |
| The 1st line of the look-up table | 1 | Float | Free | Visibility upper bound (miles) |
| The 1st line of the look-up table | 2 | Float | Free | Visibility lower bound (miles) |
| The 1st line of the look-up table | 3 | Float | Free | Rain intensity lower bound (inch/hour) |
| The 1st line of the look-up table | 4 | Float | Free | Rain intensity upper bound (inch/hour) |
| The 1st line of the look-up table | 5 | Float | Free | Snow intensity lower bound (inch/hour) |
| The 1st line of the look-up table | 6 | Float | Free | Snow intensity upper bound (inch/hour) |
| The 1st line of the look-up table | 7 | Float | Free | Speed limit reduction (mph) |
| The last line of the look-up table | 1 | Float | Free | Visibility upper bound (miles) |
| The last line of the look-up table | 2 | Float | Free | Visibility lower bound (miles) |
| The last line of the look-up table | 3 | Float | Free | Rain intensity lower bound (inch/hour) |
| The last line of the look-up table | 4 | Float | Free | Rain intensity upper bound (inch/hour) |
| The last line of the look-up table | 5 | Float | Free | Snow intensity lower bound (inch/hour) |
| The last line of the look-up table | 6 | Float | Free | Snow intensity upper bound (inch/hour) |
| The last line of the look-up table | 7 | Float | Free | Speed limit reduction (mph) |
An example vsl.dat file is shown in Figure 5-4. The first line indicates that there is only one look-up table in the file. The second line shows that the first (and the only one in this example) look-up has four rows. The third line (i.e. the first row of the look-up table) suggests that when visibility is in the range of 1 - 3 miles and there is no precipitation (e.g. fog) the speed limit should be lowered by 5 mph. The rest of the file specifies the other three rows (i.e. weather conditions and the corresponding speed limit reduction) of the look-up table.
Figure 5-4. General Format of the vsl.dat Input File