## 1 Introduction  
In-service highway concrete bridges bear vehicle loads every day, with strong dynamic coupling effects [1; 2; 3]. In order to shoulder the heavy traffic burden, multiple lanes are usually set along the transverse direction on the deck of a highway bridge. According to Chinese national traffic regulations, the speeds of vehicles running on different lanes are limited to different ranges. In China, the vehicle speed should increase if the vehicle changes its transverse position from a right lane to a left lane. For example, it is stipulated by Chinese regulations that the speed ranges are 60-90 km/h, 90-110 km/h, and 110-120 km/h for the right-most lane, the middle lane and the left-most lane, respectively, on a three-lane highway bridge. Based on years of practical experience, it has been found that the beam bodies bearing lanes with different speed ranges usually suffer from varying degrees of damage. According to Ref. [4], it was observed on a 4539 m super-large continuous concrete girder bridge put into service for around 20 years that a beam supporting vehicles running at lower speeds suffers from more severe apparent problems compared with a bridge bearing vehicles traveling at higher speeds. To reveal the mechanisms behind this scientific issue, in-depth studies were undertaken by Ref. [4] following an on-site survey. By using a numerical platform to simulate the scenarios of a vehicle running through a section of the bridge at different speeds and via comparisons between the structural responses calculated for different vehicle speeds, it was observed that the maximum dynamic responses (vehicle-induced deflection and internal force) are roughly the same between different cases. However, the vehicle load-holding duration is longer for low vehicle speeds than for high vehicle speeds. The authors of Ref. [4] concluded that the beams bearing vehicles of lower speeds are therefore of poorer quality. Regarding this problem, the present article offers a viewpoint different from Ref. [4]. According to the data reported in Ref. [4], the vehicle-induced maximum stress calculated is much lower than the material strength of the concrete, and the structure is proven to be in safe elastic states throughout the loading process. For a bridge constructed using concrete to ensure that the stress is no greater than the material strength, it is widely acknowledged that the load-holding duration does not have a significant influence on the degree of damage on the structure, as the concrete material is not prone to non-strength failures (e.g., fatigue failure). Therefore, the contention presented in Ref. [4] that the observed phenomenon is due to the vehicle load-holding duration is unreasonable. On the other hand, a drawback is also noted for the numerical simulations presented in Ref. [4]; i.e., the road surface roughness is not taken into account by the performed analyses. According to Refs. [5; 6; 7; 8], the road surface roughness has noticeable effects on the vehicle-bridge dynamic interaction. As almost all actual bridges are associated with varying degrees of road surface roughness, we have reason to suspect that the different degrees of dynamic amplification due to road surface roughness could explain why beams bearing vehicle loads running at different speeds are subjected to dynamic action of different intensities. In the past, a lot of effort has been devoted to exploring related matters of engineering, such as the vibration analysis of multi-span beams subjected to moving loads and masses [9; 10; 11; 12] and the dynamic response of bridge-like structures subjected to moving loads at a small scale [13; 14; 15; 16]. For example, [PERSON] and [PERSON] [9] developed a method based on the modal superposition and regularization technique to identify moving loads on an elastically supported multi-span continuous bridge deck. [PERSON] et al. [10] studied the dynamic response of multi-span visco-elastic thin beams subjected to a moving mass by an efficient numerical method. [PERSON] et al.