€¦ · Web view2020/08/13  · Cutting down an avenue of trees will doubtless raise local opposition. Running PRT track just a few feet past people’s windows will be opposed.

PRT Underground System

When it comes to densely packed establ ished ci t ies, Personalized Rapid Transit (PRT) advocates would do well to look at al ternatives to an elevated track. This art icle is intended to spark a discussion by laying out the concepts and some of the costs for a successful underground PRT

system. I t should be understood that the solut ion described is just one of many potential underground options - a start ing point for discussion and development.

In exist ing urban environments, the elevated tracks have many obstacles:

1) They need to clear traff ic (≥ 13’6”), including vehicles driving/parked alongside a track that cant i levers beyond a narrow sidewalk.

2) Either clear/avoid power and phonel ines or pay for the l ines to be relocated. 3) Clear/avoid street trees occupying the same sidewalk or easement. Cutt ing down

an avenue of trees wil l doubtless raise local opposit ion.4) Running PRT track just a few feet past people’s windows wi l l be opposed.5) Tracks must span roads, requir ing longer and deeper members - increased height. 6) There is a tradeoff between l ight vs heavy track – cost vs r ide quali ty and speed.7) If running above the sidewalk, there needs to be suff icient easement width for both

the columns and stat ion access from ground level. 8) Gett ing the riders up and down eff icient ly from a stat ion +15 feet in the air requires

space and mechanical assistance. With stat ions at walking intervals – expensive.

PRT Underground: Consider putt ing the track in a precast concrete tunnel just below the street pavement. As a start ing point for conversat ion I have laid out the fol lowing example.

Use precast Two-Way tunnel units. Internally 16’ wide and 6’8” high (door height). The outside dimensions (see diagram above) 17’4” across x 8’2” high x 12’ long (12’ length of tunnel). These units weigh 64,000 lb. and are opt imal for weight, and width during transport in most of the United States. 12’ wide requires a ‘Wide Load’ permit but no escort. A weight ≤ 65,000 lb. can be carr ied with a common tr iple axel t rai ler. Using a standard trai ler, 8’2” clears under al l br idges and power l ines.

This tunnel would be set direct ly below the paved street. The 10’ wide stat ion (standard lane width) would be at street level in the median. If there were no exist ing median, the roadway would deviate around the stations, narrow to minimum width and use the parking and/or some sidewalks ei ther side. This could actually be to advantage as a way to slow traff ic where the r iders are crossing. As such, a street just 38’ bui lding to bui lding, would accommodate 2x 5’ sidewalk, 2x 9’ lane and a 10’ wide stat ion.

The outer 5’4” of each side of the 16’ tunnel would accommodate north bound and south bound traff ic. The PRT pod-cars would be approximately 4’4” wide and 6’2” high al lowing 6” clearance al l round. The center 5’8” would support several functions:

1) Accommodate a simple scissor l i f t to elevate and lower the PRT pod-cars from the tunnel to the street level stat ion. This saves space, height, venti lat ion, egress, safety and cost issues of br inging the r iders down to a tunnel station.

2) From the center, pod-cars can arrive and depart f rom/into either ‘Northbound’ or ‘Southbound’ traff ic lanes, immediately taking them in the r ight direct ion.

3) The pod-car also has the f lexibi l i ty to enter and exi t the l i f t f rom either the ‘North’ or ‘South’ end. The pod-car can que in the center for unloading ei ther side of the l i f t . This increases the loiter capacity and f lexibi l i ty of the system at each stat ion.

4) Most of the remainder of the center 5’8” is for egress to Emergency Stairs.

5) Halfway between the stairs ( furthest point) are recharging stat ions for the pod-cars.

Ventilation and FireThe all e lectric system does not require much vent i lat ion except to supply a change of fresh air for passengers in the cars. Tunnel air wil l be continuously vented by fan to street level halfway between the exit stairs (where the recharging stat ions are). In case of f i re/smoke/gas, the tunnels wi l l be act ively pressurized at the Emergency Stair exi ts. As such, moving towards the exits wil l move passengers towards increasingly better air .

Also, at the midpoint between exit stairs, the system wi l l have automatic f i re doors located in the center lane to close the three “ lanes”, sealing off sections of the tunnel from the rest of the tunnel gr id.

Malfunction and Emergency Exit

The pod-cars carry their own electricity so there is no issue with a sudden power outage stopping al l pod-cars. The cars can thus move away from an area in trouble. They can also slowly move to a location suitable for exi t within a troubled area.

Should a stat ion l i f t or other stat ion equipment malfunction, the pod-cars can move to another nearby stat ion to off load their passengers.

Should a pod-car malfunct ion, the pod-car would stop, and that sect ion of track be cleared by the other pod-cars. Pod-cars behind the malfunct ioning vehicle would use the center lane to do a 2-point turn and head away from the area. Once the tunnel sect ion between the malfunctioning vehicle and the Emergency Exit is clear of other pod-cars, the doors wil l open and the passengers move in an orderly manner to EXIT stairs. An emergency crew would be dispatched to a) make sure that al l passengers were out including the disabled and strol lers, b) move the malfunct ioning vehicle into the center lane to wait for a “Tow-Pod” to transport i t to maintenance. Traff ic then resumes.

Should more than one pod-car malfunction in an area, the center lane and spacing wi l l be such that exit ing passengers can move around the stat ionary vehicles. Pod-cars already in the center lane can discharge to the empty traff ic lanes once al l pod-cars are stopped or left the area. Pod-cars wil l not be al lowed to stop in l ine with one another nor in l ine with the stat ion l i f t , stairs, f ire doors or other i tems in the center lane. The probabi l i ty is low, but should a complete breakdown cause blocked doors, the system wi l l send an empty pod-car/s to push the disabled vehicle clear of the obstacle. Maintenance crews wi l l assist.

Interchanging between crossing tracks to create 2 dimensional grid service Given smart onboard sensors in conjunction with system-wide choreography, the PRT Underground system can use a simple but effect ive traff ic circle “roundabout” to al low intersect ing tunnel “streets” to either cross or change “streets”. This avoids complex track switching and the delay t ime for pod-cars wait ing for the switching to occur before proceeding. The t iming choreography would be computer control led with onboard anti-coll is ion backup. The “Roundabout” el iminates one tunnel needing to be deeper than the other to cross (problem for subways). I t also el iminates the need to get off a “North-South” l ine and change to an “East-West” l ine. It al lows a pod-car to be a point-to-point del ivery anywhere in the PRT tunnel gr id .

This f lexible transportat ion grid al lows pod-cars to take alternate routes if there is a breakdown/malfunction or traff ic congest ion in a sect ion of the system – similar to a human or “Garmin” GPS wil l take an al ternate route. It may also offer al ternate stat ions.

“Roundabouts” can be made in repet it ive, transportable precast sect ions. Where customizat ion is needed, small sect ions can be cast- in-place.

Track, Pod-cars and Track GuidanceThe tunnel would al low a relat ively simple, stable 4-wheel vehicle. Traveling on a track set on solid ground wil l negate “beam-bounce” issues al lowing faster speeds and better r ide qual ity. The f loor joints between the precast sect ions would be diamond ground using laser guidance to be smooth and eliminate any bumps. This is a wel l-established technology used on modern concrete freeways.

Pod-Cars would run on a “Tesla-l ike” battery giving +/- 8 hours of run t ime. Between peak t imes when not al l pod-cars are needed, they wil l recharge. To do this the pod-cars wi l l park in designated areas of the center lane furthest from stairs, thus not an obstruction to egress. Whi le empty and charging, they wil l also electr ical ly sanit ize the vehicle by turning on UV l ights and/or an ozone generator (used in those CPAP cleaners on TV). Battery power el iminates the expense of electr i fying the ent ire track and having the expense and maintenance of an electr ical pickup on the track and pod-car. I t a lso al lows power while changing lanes. Isolated recharging electrical pickup to an area furthest from the emergency exi t stairs negates a safety issue with emergency egress passengers.

Existing PRT guidance and controls, along with dr iverless car and driverless parking technology would be adapted for the pod-cars. This is part icular ly appl icable for moving in and out of the wait ing areas and station in the middle lane.

During main transit , the system could use one edge of the precast tunnel as a physical guide. Coded markers on the f loor or cei l ing would give precise “mi le-marker” locat ions. This would give an exact and cont inuing update of locat ion within and along the tunnel. 2D location at and around the stat ions or in the center lane would use short range tr iangulating beacons plus posit ioning markers on the f loor of the tunnel.

Schedule and Cost

Below are some examples of Tindall Corporations precast tunnels. Fast and economical construction. A crane and crew of f ive set an average of two pieces an hour. In our example, that would be a mile of 12’ PRT tunnel units in about 6 weeks (greenf ield). In ‘downtown’ sett ing planning on one section per hour would be appropriate.

My budget numbering of the precast sections above, delivered to site would be about $16,000 per 12’ sect ion length (+/- 10%) => $7 mil l ion/mile and $1 mil l ion/mile (+/- 30%) to instal l and waterproof. You would then have to al low a l i t t le extra for al terat ions to the precast units for the stat ions and stairs. The “roundabout” interchanges would budget at $100,000 each (+/- 30%).

Street excavat ion, backf i l l and resurfacing road wil l depend upon which city i t is. For instance, 5 t h Avenue Manhattan NY would be more expensive than Main Street, Greenvil le SC. Undulat ion of the street would also be a factor. For instance, San Francisco would be more chal lenging than Houston. Were it “Greenf ield” the excavat ion itself is not overly dif f icul t or expensive.

The most chal lenging ut i l i t ies you need to relocate would typical ly be the sewer and storm water piping given they use gravi ty and r iser pumps. Drinking water is under pressure, so relat ively easy to reroute underneath. Again, this would need to be assessed on a case by case basis.

Money would need to be budgeted for the scissor l i f ts, sensors and other electr ical plus, of course, the pod-cars themselves. I wil l leave the costing of th is aspect up to the experts in this f ield.

Similar concept – Grander Scale

Although I thought of the above PRT Underground concept ten years ago. Recently Elon Musk’s “Boring Company” has used a similar concept but on a much grander scale and grander cost.

Summary and Discussion

The above art icle is intended to spark a discussion as to how an Underground PRT system might look. Without making the art icle too voluminous, I have tr ied to address key aspects of a viable system. This part icular system is not intended to be for high speeds and long distance. I t is intended to create a network grid in a one to two mile area of a city. This gr id could then deliver passengers to other transportat ion networks for metropol itan or interci ty r ides.

I have no doubt that some readers wi l l take issue on some of the detai ls or lack thereof. Some wi l l have questions on how the system described would address specif ic situat ions. That ’s al l OK. The big thing is that I ’ve got you thinking.

Jim SchroderDevelopment Manager – Industrial [email protected] Corporation www.TindallCorp.com