Tag Archives: speed

Smartphone App Alerts Drivers Exceeding Speed Limits on Curves

Researchers have developed a proof-of-concept curve speed warning system for use with mobile phones, a technology they hope car manufacturers might adopt for in-vehicle systems. The proof-of-concept system uses data from local road agencies on curve locations, speed limits and signage with geofencing to trigger cloud-based data alerts to road users driving faster than recommended speeds for curves.

What Was the Need?

Over one-quarter of fatal highway crashes occur at horizontal curves. In Minnesota, these areas are a contributing secondary factor in 49 percent of fatal crashes. Each year, accidents on two-lane, two-way highway curves injure over 4,000 people and result in 70 deaths, almost one-fifth of annual roadway fatalities in the state.

Research has shown that dynamic message signs with speed detection components work well in warning drivers to reduce speeds, but these systems require power supplies and cost approximately $14,000 per site. Minnesota’s Otter Tail County alone has over 400 reduced speed curve sites. The Local Road Research Board (LRRB) and MnDOT have been funding research that examines alternative approaches to speed warning systems for drivers approaching curves.

“This smartphone application stitches together existing technologies for GPS, GIS and mapping to provide an inexpensive, cloud-based warning system for drivers,” said Richard West, public works director, Otter Tail County.

In a 2015 study, researchers developed an in-vehicle, vibration-based warning system tested in a driving simulator that relies on data from highway sensors and other sources. Research in 2018 focused on the use of GPS signals to calculate and recalculate a vehicle’s trajectory on roadways to issue warnings. A new phase of this study is refining the approach to draw on vehicle-to-vehicle data.   

What Was Our Goal?

The goal of this research was to develop a dynamic curve speed warning system that would employ cloud-based data sharing. The system would not require significant infrastructure investment and would be applicable to all reduced speed curves in the MnDOT highway system.

What Did We Do?

Following a literature search, researchers focused on developing a proof-of-concept smartphone app that would warn drivers of upcoming curves and speed reduction requirements. They also created a database for county road agency managers to input curve locations within their jurisdictions, speed limits and sign facing direction for use with the smartphone app.

Researchers layered the database into their geographic roadway inventory tool, which draws on GPS and mapping data, and combined data from the sources into a cloud-based curve database. Then they developed a geofence system that triggers alerts as the tracking device crosses virtual geographic boundaries.

A smartphone app uses GPS and GIS to trigger a warning via the cloud to smartphone users traveling above the curve speed limit as they pass through a geofence, or virtual geographic boundary, before the curve.

An illustration of the system overview that includes a curved road with geofencing overlays marking two warning areas on the curve, a cloud-based warning database and a smartphone screen showing a “Reduce speed” message.
A smartphone app uses GPS and GIS to trigger a warning via the cloud to smartphone users traveling above the curve speed limit as they pass through a geofence, or virtual geographic boundary, before the curve.

The curve speed warning system was tested on roadways in Otter Tail and Pope counties. After county agencies input curve location and speed limit data into the system, researchers tested the system by running the app while driving a number of highways selected for a high density of reduced speed curves. They adjusted the system based on these field tests to accommodate GPS signal speed, travel speed and cloud data transfer bandwidth.  

Researchers then evaluated roadside dynamic speed warning system safety impacts to determine the potential safety and cost benefits from the cloud-based warning system.

What Did We Learn?

The curve speed warning system worked in proof of concept. GPS and cloud data can be drawn on fast enough to provide warnings in time for drivers to respond. Researchers refined geofencing parameters to only pull data for curves within 30 miles of the vehicle to keep data volumes to manageable levels within standard parameters for mobile phone data packages.

“Study results show that this system works accurately. If data from county and state roads were input, the application could be made available to everybody,” said Bradley Wentz, program director, Advanced Traffic Analysis Center, Upper Great Plains Transportation Institute, North Dakota State University.

The core of the system is the curve database, which requires accurate data input by county road agencies. Testing resulted in one performance error, which was traced to incorrect data for the facing direction of a warning sign.

Image of the secondary warning on a smartphone screen showing the message “Slow Down,” the recommended speed of 45 mph and the driver’s current speed of 51 mph in a red circle.
The smartphone app sends a second warning with this message and an audible signal to a driver’s phone.

When vehicles are traveling faster than the speed limit for an upcoming curve, the smartphone app issues a silent, on-screen warning of the approaching curve and speed limit. If the vehicle does not slow its speed sufficiently, the app flashes and issues another warning with an audible signal. 

The smartphone app sends a second warning with this message and an audible signal to a driver’s phone.

Safety implications may match crash and speed reductions identified in research on the safety benefits of dynamic sign warning systems. Researchers believe the cost to maintain the software and warning database roughly matches the cost to maintain a traditional dynamic speed warning sign system. But using a single cloud-based system for the entire roadway inventory offers a dramatic cost savings over installing expensive warning sign systems at every curve.

What’s Next?

Researchers have prepared presentations for local audiences and presented findings at the 2018 National Rural ITS Conference. County road agencies can easily update the database, and the system can accommodate not just reduced speed curve locations, but any reduced speed needs, such as seasonal bumps and cracks in pavement, work zones, special events and controlled intersections.

This post pertains to Report 2019-19, “Cloud-Based Dynamic Warning System,” published June 2019. For more information, visit the research project page.

Speed Notification System Warns Drivers Approaching Urban Work Zones

Using an innovative method to calculate vehicle trajectories and gather large amounts of driver data, researchers tested and evaluated the new Smart Work Zone Speed Notification system and determined that its messages successfully influenced drivers to reduce their speed. 

What Was the Need?

Maintenance and construction on Minnesota’s roadways often create travel disruption for drivers through traffic slowdowns and queuing. MnDOT has previously tested systems to inform drivers of traffic backups in rural work zones, but slowdowns near complex urban work zones are less predictable. Drivers traveling at highway speed may come upon congestion suddenly, resulting in abrupt braking and the risk of rear-end collisions. 

Posting advisory speed limit messages near these work zones has not been effective. To address the problem, MnDOT developed a Smart Work Zone Speed Notification (SWZSN) system designed to inform drivers of the actual speed of slowed downstream traffic near large urban work zones. Researchers from the Minnesota Traffic Observatory then tested and evaluated this system over time in an actual urban highway construction work zone. 

What Was Our Goal?

The primary objectives of the project were to quantify the speed notification system’s effect on drivers’ behavior and determine its impact on the safety of the work zone. With an effective work zone speed notification system, MnDOT’s goal was to create safer work zones by giving highway drivers real-time information that would influence them to slow down adequately before a congestion hazard, avoiding dangerous braking and collisions. 

What Did We Do?

A variable message sign, part of the SWZSN, displays the warning “Slow Traffic Ahead” in a construction zone.

The SWZSN was designed to collect traffic speed data throughout a work zone and run it through an algorithm, generating the appropriate message for drivers on a variable message sign, such as “35 MPH 1 Mile Ahead” or “Stopped Traffic Ahead.” 

MnDOT wanted to deploy the system within a project replacing 4.4 miles of Interstate 94 (I-94) east of downtown St. Paul. The construction was to be completed in stages between spring 2016 and fall 2017. This large project would include many lane closures and expected traffic congestion; the new system could mitigate some of the traffic disruption. The deployment and evaluation of the SWZSN took place in three phases:

  • Pre-SWZSN deployment (mid-2016): Gathering data from the work zone before the system was deployed to obtain data demonstrating drivers’ behavior and crash frequency data without the new system.
  • Post-SWZSN Phase I deployment (2016 into 2017): Gathering the same data from the work zone after the SWZSN was deployed.
  • Post-SWZSN Phase II deployment (the entire 2017 work season): Gathering data from the work zone after initial deployment, with troubleshooting and improvements of algorithms and messages in place, showing drivers’ behavior and work zone crash frequency with the improved SWZSN and the analyses of these data. 
A variable message sign, part of the SWZSN, displays the warning “Slow Traffic Ahead” in a construction zone.
Speed detection sensors were installed on poles every half-mile through a new highway construction work zone.

To collect data for the system, MnDOT’s Regional Transportation Management Center mounted Wavetronix speed detection sensors on poles every half-mile in the work zone, replacing old loop detectors. Researchers also deployed nine solar-powered cameras on mobile trailers about every half-mile. This allowed researchers to capture traffic flow images in more strategic locations where traffic queues were forming since the construction zones were complex, crowded and often changing, with many visual obstructions. Data were transferred primarily via an arranged wireless radio link to the Minnesota Traffic Observatory. 

Researchers then applied their own innovative methodology—a Trajectory Extraction Tool (TET)—to the traffic images captured by the cameras using video alone to calculate a vehicle’s deceleration rate when approaching traffic congestion. The cameras were positioned to optimize TET performance. Researchers gathered tens of thousands of data points for analysis from traffic in the work zone over the course of the project. 

What Did We Learn?

During the first year of SWZSN implementation, the project team identified discrepancies in the speed notification algorithm, such as unreasonable or delayed messages. By the second construction season, those anomalies were significantly reduced. The most significant results of this project showed that in situations where messages communicated to drivers were consistent and accurate, reductions of more than 30 percent in the selected deceleration rates were observed.

Most importantly, the speed notification system is clearly noticed by drivers and results in a statistically significant influence on drivers’ behavior, suggesting that downstream speed notification is an effective traffic control tool.

What’s Next?

This evaluation project was considered a success: The system is more effective than previously used work zone advisory speed limits. The SWZSN has already been deployed in two highway construction sites and will be used for future projects.

This Technical Summary pertains to Report 2019-21, “Evaluation of the Smart Work Zone Speed Notification System,” published June 2019. Visit the MnDOT research project page for more information.