Plaintiff appeals from a verdict and judgment for fendants following trial of his damage action for irsonal injuries sustained in a motor vehicle acci-nt.
Plaintiff makes the following assignments of error:
1) Failure to give the uniform jury instruction1 garding the right of every person to assume that the rw will be obeyed;
2) Refusal to admit proffered expert testimony of 70 witnesses, Leonard Schultz and James Isaac.
The essential facts are:
The accident occurred during daylight hours at a ’ intersection in Clackamas County, being the inter-ction of Highway 224, an arterial highway, and ikers Ferry Road, an access road. A stop sign posted the intersection required all traffic entering Highly 224 from Bakers Ferry Road to stop.
Plaintiff was driving a passenger auto and was aveling on the arterial highway at the rate of 55 ties per hour. Defendants, who are husband and fe, were approaching the intersection on Bakers rry Road and were each operating a truck— tractor ¡th a large belly dump trailer attached. The front icle, which was being driven by the wife, was ing the back one, which was disabled and was ing steered by the husband. The two vehicles were ined together by a steel chain about 10 feet long, king in effect one continuous chain of vehicles iroximately 77 feet in length.
I Wife, after coming to a stop at the intersection and Iking both ways on Highway 224 for approximately |o minutes, entered the highway and turned left. *544Moments after she had turned, plaintiff’s auto struck the rear tires of the last dump trailer. Both trucks were operating their red-flashing hazard lights at the time.
Plaintiff testified that when he saw the first vehicle enter the highway, he slowed but did not immediately see the second one; that when he did see the second one he assumed that it was going to stop at the stop sign; that he saw no flag or warning device on the tow chain; that before he could stop his car he collided with the second tractor-dump truck being driven by the husband. There was a grocery store located at the intersection in such a position as to prevent plaintiff from seeing the defendant husband’s vehicle as the defendant wife was waiting to enter the arterial highway.
Plaintiff alleged that the collision was a result of defendant’s negligence, inter alia, in (a) operating a combination of vehicles exceeding a length of 50 feet; (b) failing to display a red flag upon the tow chain between the towed vehicle combination and the towing vehicle combination.
The expert witnesses proffered by plaintiff would have testified on the impropriety of defendants’ towing arrangement, namely that it was contrary to the usual and customary method, i.e., that the customary practice is to break down the combination of vehicles and tow the tractor and dump trailer separately. The trial judge, however, sustained defendants’ objections to this testimony, saying that it was not a proper subject for expert testimony "because I think it’s a decision which can be arrived at by ordinary people who sit as jurors.”
The judge refused to give Uniform Instruction No. 10.05. However, he gave the following instruction:
"The law presumes that all persons have obeyed the law and have been free from negligence. Accordingly, the mere fact that an accident occurred or that a party sustained injury or damage is no indication of negligence on the part of anyone. * * Uniform Instruction 10.01.
*545Plaintiff argues that the accident was caused by vo law violations by defendants: (1) failing to affix a id flag on the tow chain between the two vehicles as squired by ORS 483.508(3), and (2) operating a combi-ition of vehicles over 50 feet in length without a srmit or special county authorization, ORS 53.504(4).
Plaintiff cites Smith v. Holst, 275 Or 29, 549 P2d 671 (1976), in which our Supreme Court held that ilure to give an instruction regarding the right of ery person to assume that the law will be obeyed [inform Instruction No. 10.05) in a motor vehicle cident case was reversible error.
Defendants answer the above by averring that dther of the above supposed violations was a proxiate cause of the accident, which was purely plain-f’s own negligence; that the 50 foot limitation does t apply to towed vehicles, citing Cavett v. Pac. Greyhound Lines et al., 178 Or 363, 378, 167 P2d 941 (1946).
Taking up plaintiff’s first assignment, we conclude at it was reversible error not to give the requested struction (No. 10.05) regarding the right of every person to assume that the law will be obeyed. Smith v. Holst, supra.
We cannot say on the facts presented here that isonable minds could not have concluded that the itutory violations regarding overlength vehicles and lure to place a red flag on the connection between ving vehicles and disabled vehicles caused or con-buted to the occurrence of the accident. We do not fard the rule in Cavett exempting towed vehicles m the maximum length statutes as applying to the ;e at bar and thus exempting defendants from the •visions of ORS 483.504(4).
As to plaintiff’s second assignment, we are of the nion that the trial court also erred in refusing to omit the proffered expert testimony. In Koch v. Southem Pacific Co., 266 Or 335, 513 P2d 770 (1973), *546the court held that experts could testify as to the aspects of a railroad crossing which increased its danger to vehicular traffic, and as to steps the defendant railroad could have taken to alleviate the danger.
Similarly, in Tijerina v. Cornelius Christian Ch., 273 Or 58, 539 P2d 634 (1975), our Supreme Court approved of the use of expert testimony in the proper preparation and maintenance of softball and baseball fields. The court observed:
"The test for the admissibility of expert testimony is whether the jury can receive appreciable help from it. The proper preparation and maintenance of softball and baseball diamonds must take into account the manner in which the players might use the field, the dangers to which they are exposed, and the measures necessary to avoid injury in the course of play. Although many jurors may know of these factors, many may not. Those who do not could receive appreciable help in assessing the minimum standard of maintenance for softball playing fields. Therefore, we are of the opinion that the expert testimony in this case to which defendant objects was admissible.” 273 Or at 66. (Footnote omitted.)
Reversed and remanded.
"Every person has the right to assume that others will obey the llaw, unless and until such person knows or should in the exercise of reasonable care know the contrary.” Uniform Instruction 10.05.