There are a lot of layers to your question. I can accept the premise that rail transport was more efficient for military purposes in continental Europe during and prior to WW2 for any number of reasons.
However, IMO, which is backed by military experience, it is not more effective . I think Ike would have recognized and considered this.
Rail transport limits combat power by restricting the ability to project force. A unit carrying out movement by train is definitely not able to employ it's full combat power freely.
1. Loading and Unloading material for rail transport(Tanks, Vehicles, Artillery, Etc.) requires specialized equipment and facilities.
A unit in transit by rail can't simply deploy its resources in response to an attack on route. Nor can it reroute to another location in response to new developments.
This is fine for infantry units, who ultimately can deploy the the majority of their combat power independently of logistical or mechanized support for limited periods of time. For the vast majority of units however this is not ideal due to their training and equipment (or lack thereof) which is driven toward employing the equipment they cannot effectively access.
2. Personnel and Material transported by rail can expect greater degree of loss in the event of an incident.
Everything and everyone inside a train is going to be effected by any incident. Rail transport in peace time is safe, but during war it will become significantly less so as part of a nation's military infrastructure and supply chain.
So if the train gets hit, everything on the train is effected. Compare this to a convoy traveling via road. If one vehicle gets hit the others do not always get taken out, damaged or otherwise see a degradation of combat power.
Simultaneously, they retain a greater degree of flexibility to respond as discussed below. meaning that the severity of any incident is likely to be lower.
3. Corollary to the above, personnel transported by rail have limited response options (TTPs) in the event of attack or accident to prevent loss of men and material.
In the event that a train gets hit, even if it's only stopped, the material and personnel on board are out of the fight until recovery operations can be carried out.
They're likely limited to defensive operations with small arms and squad automatic weapons, supplemented by foot patrols (very risky) for the duration. Compare this to roadway transport, which can reroute as practical and can deploy a greater degree of it's combat power more readily to clear obstacles, conduct recovery or defend their position.
4. While the difficulties listed above can be overcome, doing so drains combat power and resources from offensive operations and therefore eliminates the efficiency of rail transport.
All the difficulties listed above could be overcome with sufficient effort. For instance, the risk of aerial attack could be negated by installing flak cannons and screening movements with aerial support. But doing that removes those guns and planes from the front lines, which can only be overcome by building more guns, more planes and paying more men to operate them.
The specialized facilities could be overcome by say, building cranes onto the rail cars. Doing so introduces complexity, which increases cost, maintenance and risk of failure, while increasing the amount of labor required.
Alternatively more transfer terminals could be constructed but again you're increasingly complexity and adding cost and labor, worse yet you're ensuring that these costs will be ongoing, even in peacetime, so then civilian customers have to bear the burden or your military infrastructure will fail.
You could enable units to respond with greater flexibility through force reorganization and training, but again, you're talking about massive back end costs.
Roads are cheaper to build. Cheaper to maintain. Roadway transport reduces a unit's combat power very little and in doing so does not add additional complexity or costs as result.
When compared to what I consider the gold standard of military transportation, aerial - after all a plane in flight is a plane in the fight - the insterstate highway system comes much closer than railway transport to maintaining combat power and force projection capability while simultaneously effecting movements.