The emphasis on transportation is vital when dealing with modular buildings. The various modes used today carry both pros and cons among industry professionals. The detail in this level of modular transportation produce three widely used modes of transportation, and in the purpose of this discussion will be to use the below terminology to describe the three modes; Expandable Low-Bow Tractor & Trailer, Axles, Tires & Hitches, and Custom Carrier Trailer. Successful modular projects occur when transportation is emphasized from sales to estimating to design, through construction and to the final transportation and site erection.
EXPANDABLE LOW-BOW TRACTOR & TRAILER
This method uses rather specialized over-the-road tractor and trailers and the type, length and number of axles required by the trailer are determined by the size and weight of the modular piece. No hitch or axles are installed on the modular piece for this application. Upon delivery the truck and trailer are leased when the piece is unloaded.
PROS OF EXPANDABLE LOW-BOW
Heavy modular weights can be achieved much easier with this mode of transportation.
In some regions of the country, this mode allows for some transportation laws regarding overall shipping height to be less restrictive..
These trailers have air-ride suspension, thus putting the modular piece under the least amount of stress and vibration of any mode of transportation. This can reduce stress cracking and other shipping related damage claims. There can also be a slight design advantage to not over-designing structurally for transportation forces vs. other modes of transportation.
This mode is broadly available and more often than not has many options for trailers and semi-trucks well equipped for this purpose throughout the country. This is best for large modular deliveries where it's required that numerous pieces a day are being delivered on consecutive days for maximum schedule advantage.
CONS OF EXPANDABLE LOW-BOW
Cost, depending on transportation destination, can be as much as 40% higher on face value, when comparing gross costs and no other cost benefit analysis is completed between modes.
The typical length of expandable trailers max out at the dropped area (known as the well) of 49 feet; some can go up to 60 feet, but availability is limited and may increase cost.
Turning radius requirements for this mode is slightly greater, depending on modular piece length, due to the axles on these trailers being behind the well. This can complicate site access and routing when delivering in tight urban areas.
A crane is required at site to remove the modular piece from the trailer.
AXLES, TIRES, AND HITCHES
This method employs several axles, depending on size and weight of the modular piece, typically rated at a maximum of 5,000 lbs. each. However, tire limitations bring them down closer to approximately 4,200 lbs. each. Hitch and Axles are designed and installed as either detachable or permanent in nature depending on the modular application, which is then transported down the road by a semi-tractor and no additional trailer is required.
PROS OF AXLES, TIRES, & HITCHES
Compared to a Low-Boy, generally less expensive from a gross transportation only price.
Compared to Low-Boy, this method has a tighter turning radius during delivery.
In some instances, modules can be erected on a single-story foundation without the use of a crane on site.
Modular lengths in excess of 60 feet can be achieved if within weight carrying capabilities of the axles.
CONS OF AXLES, TIRES, & HITCHES
Heavy modular weights cannot be accomplished with this mode of transportation, especially when concrete floor non-combustible designs are required.
Certain states have special height restrictions with this method, that are less than could be achieved on low-boy mode of transportation.
Due to the delivery system being on an axle-spring the modular unit is exposed to increased deflection and vibration. This can increase design/steel costs and can result in an increase in transportation damage claims.
Imbalanced load in the design of a modular section can be challenging to engineer the axle location to compensate, and in extreme cases not possible.
When load reach near minimum weights blowing out tires during transport can be a common occurrence resulting in possible delivery schedule delays.
When the axle method is used on a slab on grade foundation or for multi-story time/costs in the erection must be maintained to remove hitches and axles as they are set in place.
With this mode, unless cost is incurred to ship back removed axles and hitches for reuse, they are considered a one-time use cost which reduces the overall cost effectiveness of this mode of transportation.
Typically when this mode is used, there will be some field repair work of the floor insulation system were the tires are located.
CUSTOM CARRIER TRAILER
This method employs a custom built carrier trailer that is sized for a modular piece size and weight, it is equipped with a axles, tires and a hitch designed to support the modular unit size and is transported down the road by a semi-tractor and no additional trailer is required. Upon delivery the modular piece is removed from the carrier and it is returned to the of site construction facility to be re-used.
PROS OF CUSTOM CARRIER TRAILER
Generally, the least expensive from a gross transportation only price; that is if you do not consider the capital cost of building and maintaining a fleet of custom carriers, because you will not need to purchase hitches, axles and tires for each piece.
Tighter turning radius during delivery than low-boy.
In some instances, modules can be erected on a single-story foundation without the use of a crane on site.
Modular lengths in excess of 60’ can be achieved if within weight carrying capabilities of the axles.
CONS OF CUSTOM CARRIER TRAILER
Heavy modular weights cannot be accomplished with this mode of transportation, especially when concrete floor non-combustible designs are required.
To make this mode cost effective, the modular product sizes and weights need to be somewhat more consistent than with low-boy delivery.
Due to the delivery system being on an axle spring the modular unit is exposed to increased deflection and vibration. This can increase design/steel costs and can result in an increase in transportation damage claims.
Imbalanced load in the design of a modular section can be challenging to engineer the axle location to compensate.
When the load reaches near minimum weights, blowing out tires during transport can be a common occurrence - resulting in delivery schedule delays and extra costs.
With this mode, costs to return the carrier will be incurred.
There will be capital costs for constructing a fleet of carriers, licensing them, maintaining and storing them when not in use.
On very large projects requiring aggressive delivery schedules of multiple modules a day, there will be limitation by the size of the carrier fleet and the time to return carriers from the site to be reloaded, depending on travel distance this can be detrimental to the erection schedule.
While blogs are not intended to be opinion pieces, with 30+ years of modular transportation experience, my personal conclusion of this topic is in favor of the Low-Boy trailer delivery. Compared to many others, the up-front transportation cost pushes them to the other two modes discussed in this piece, but my experience bears out that in the long run Low-Boy delivery is the most reliable and least detrimental to the product and is my first choice if a project budget can allow it.
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Regards,
Lee Bachman
leebachman@modlogiq.com
MODLOGIQ Design Dept. Manager