Using Hybrid LiDAR for Positive Train Control (PTC) Systems

A 4.172Mb PDF of this article as it appeared in the magazine complete with images is available by clicking HERE

On May 12, 2015 an Amtrak Train from Washington D.C going to New York City derailed and crash on the Northeast Corridor in Port Richmond, Philadelphia. There were 243 people aboard including 5 crew members. There was a total of 200 injured (11 critically) and 8 deaths. At the time of the derailment the train was traveling at 102 mph in a 50 mph zone. This was in an area of curved track.

The derailment was significant enough to disrupt train service for several days. There wasn’t enough emergency personnel to help the injured, so several passengers and local residents had to assist in the rescue. Many of the injured had to be extracted from the wrecked cars. Five hospitals treated the injured.

There was a similar train derailment on the same curved section of tracks that killed 79 and injured 117 in 1943. The 2015 crash was the deadliest on the Northeast Corridor since 1987, when 16 people died near Baltimore.

Federal authorities from the National Transportation Safety Board (NTSB) believe the derailment was most likely accidental, and are investigating the cause of the derailment. There was speculation that the operator was distracted at the time of the accident. Officials believe that the accident most likely could have been prevented by PTC (Positive Train Control), a computerized train operation system that controls the train and trains with in a given rail network. PTC takes the human element out of operating the train. PTC was operational elsewhere on the Northeast Corridor, but activation at the crash site was delayed due to regulatory requirements.

PTC is a processor-based/communication train control system designed to prevent train accidents. PTC is both Voluntary and mandated by Title 49 Code of Federal Regulations (CFR) Part 236, Subpart Hstandards for Processor-Based Signal and Train Control Systems or by the Rail Safety Improvement ACT of 2008 Developed and implemented by a railroad following the requirements of by Title 49 Code of Federal Regulations (CFR) Part 236, subpart IPositive Train Control Systems.

PTC is currently required to be installed and implemented on Class I railroad main lines over which poisonous and toxic hazardous materials are transported and on any railroad’s main lines over which regularly scheduled passenger intercity or commuter operations are conducted. This equals roughly 70,000 miles of track and 20,000 Locomotives. This basically includes all heavy commuter rail currently. The regulatory requirement was to be mandated by the by December 31,2015 but this deadline provided to be arbitrary and unworkable for many rail owners so as a result of H.R.38 19- Surface Transportation Extension Act of 2015 the deadline was extended to December 31,2018.

PTC systems are capable of fully automatically controlling trains should an operator fails to properly operate a train. The PTC can stop, brake, and accelerate a train before an accident occurs. The PTC systems must reliably and functionally prevent train collisions, over speed derailments, incursion into an established work zone, movement through a main line switch in the improper position, and other functions warranted if applicable. They must also provide for interoperability in a manner that allows for equipped locomotives traversing other railroad’s PTCequipped territories to communicate with and respond to that railroads PTC system, including uninterrupted movements over property boundaries.

Currently, there are many options for providing data for PTC. Two of these options are collecting survey information using GPS or providing information derived from remoted sensing such as LiDAR and imagery. Merrick & Company is currently working with Maser Consulting and Xorail to provide hybrid LiDAR and Imagery data for PTC. Both options require some level of coordination with the railroad based on train activity. Training is required for anyone doing work on rails prior to doing work. Additionally, watchers are usually required during the collection of data on railroads. The collection must occur around the train schedules and even with remote sensed data there is some level of survey required so there is no getting around the daily operation of the trains. Depending on the rail operator the solution requested will vary. Additionally, the data collected is used for other proposes depending on what is collected for PTC.

The Merrick-MaserXorail team is currently working on many PTC projects together. Merrick provides the aerial information for these projects. Maser Consulting provides the mobile LiDAR information for these projects. Xorail provides the analysis and programmatic compilation, and track verify for these projects. The hybrid approach includes the collection of Mobile LiDAR, Airborne LiDAR, Ortho imagery, oblique imagery, and survey information. The complexity of the collection is a function of the complexity of the rail network. Typically, the mobile collection will consist of collection all tunnels and tunnels are defined as anything that isn’t visible from above. The mobile collection is extended beyond the tunnels to accommodate tying the mobile data to the aerial data. The aerial data is collected using the High Definition Mapping System (HDMS), which is a multi-sensor pod system mounted in a helicopter. This system includes a LiDAR Sensor, nadir look medium format digital camera and an oblique camera system. The survey will be conducted to collect control in the tunnels to reference the mobile data and additional control will be surveyed to control the aerial data. The survey ties all the control together to improve the overall results of the hybrid approach.

The required accuracy for PTC is not what one would expect but the more accurate the collection the better the result. Also, the data is collected and delivered in Latitude, longitude, WGS84 With ellipsoid heights. This is because the resulting PTC computer system on the train is equipped with a GPS system once the train is operating the PTC. The relative accuracy seems to be more important than the absolute accuracy. The required absolute horizontal accuracy of the data is 1.31m @95% and the absolute vertical accuracy is 0.80m @95%. Typically, The hybrid approach yields significantly higher results than this and in the neighborhood of 15cm horizontally and 6cm vertically. The team stated above does both the GPS approach and hybrid approach to PTC depending on client requirements. Typically, the GPS approach is more time consuming and less accurate to the hybrid approach.

In a GPS approach the track and assets that relate to PTC are all GPS surveyed in using Kinematic collection along the rail center line and the assets are surveyed using RTK. The GPS survey typically will take roughly 30 days for about 120 miles of track including an extensive number of assets and the rail center line. This similar collection using a hybrid approach will take significantly less time. The GPS approach requires additional track scheduling, training, and required watchers during collection to make sure there is no interference with the trains. Additionally, centerline collection requires working around the train schedule and typically is done very late in the night. The hybrid approach requires some track scheduling, training and watching but it is significantly less. Typically, scheduling, training and watchers are required when the mobile sensor is collecting in the tunnel areas. Depending on control locations for the reference survey there is a requirement for scheduling or watchers or both. Typically, the required reference survey for the aerial will need minimal scheduling or watchers, if any but training is usually required. The GPS approach depending on surrounding environment may require additional collections as a result of bad GPS results. The biggest error source is cause when collecting the centerline information for PTC as a result of elevation masking, cycle slips and loss of lock. This is caused by tree canopy, buildings, bridges and similar features. It is unclear if catenary above the track when present interferes with the GPS solution because several kinematic surveys have been conducted under overhead lines with acceptable results. The potential exists but as a result of the required accuracies this interference maybe in the noise when the GPS approach is used. Results from the hybrid approach show no signs of magnetic field interference from the catenary in the mobile data and this maybe a result of having an IMU and DMI in addition to two GPS antenna which gather attitude, directional and velocity information that is combined in to get the positional solution. In the case of complete GPS loss the sensor relies on the IMU, DMI and surveyed targets in these area. There is no impact on the aerial collection.

PTC requires several assets to be extracted from the data including the centerline. The asset extract includes but is not limited to the following, main line tracks, yard limits, spur tracks, mile post markers, clearance points, horizontal curve, railroad grade crossings, grade of track, signals, turnouts, point of switches, time table speeds, begin/ end milepost, DOT number, type of crossing, Horn disable, bridges, tunnels, station platforms, bungalow, cases, antenna towers in the ROW and WIU locations. Typically, the turnaround time for extraction is very strict.

Once the data is extracted and compiled into the PTC there is a process to track verify the PTC. This step is very important to making sure that all assets and everything related to the operation of the train and track is as it exists so that the PTC functions as designed. An elaborate video system is used to verify the PTC used on a rail car.

PTC is an integral part of train safety and has proven very effective in preventing train wrecks. The federal government has extended the deadline for implementation of PTC as required at the request of the rail owners to insure that proper systems are in place to operate all required commuter trains and hazardous material train as safely as possible. LiDAR, GPS and other remote sensing technologies are playing an important part in insuring these systems have the necessary data to fully comply with the regulations and save countless lives as a result of this solution.

James Wilder Young (Jamie) CP, CMS-L, GISP is currently a Senior Geomatics Technologist for Merrick & Co. located in Greenwood Village, Colorado. His experience includes all aspects of LiDAR including sensor development, applications development, data acquisition, data processing and project management.

A 4.172Mb PDF of this article as it appeared in the magazine complete with images is available by clicking HERE