@Html.AccessibleValidationMessageFor(m => m.DeliveryMethod)
@foreach (var deliveryMethod in Model.GetDeliveryMethodsOrdered())
{
    @Html.AccessibleRadioButtonFor(m => m.DeliveryMethod, deliveryMethod.Id, new { id = string.Format("DeliveryMethod_{0}", deliveryMethod.Id) })
    <label for="DeliveryMethod_@deliveryMethod.Id">@deliveryMethod.Description</label>
}

public static IHtmlString AccessibleRadioButtonFor<TModel, TProperty>(this HtmlHelper<TModel> html, Expression<Func<TModel, TProperty>> expression, object values, object htmlAttributes = null)
    {
        ModelMetadata metadata = ModelMetadata.FromLambdaExpression(expression, html.ViewData);



        var fieldName = ExpressionHelper.GetExpressionText(expression);
        var fullBindingName = html.ViewContext.ViewData.TemplateInfo.GetFullHtmlFieldName(fieldName);
        var validationAttributes = html.GetUnobtrusiveValidationAttributes(fullBindingName, metadata);
        if (!html.ViewData.ModelState.IsValidField(fullBindingName))
        {
            if (!validationAttributes.ContainsKey("aria-describedby"))
            {
                validationAttributes.Add("aria-describedby", fullBindingName.ToLower() + "-valMsg");
                validationAttributes.Add("aria-invalid", "true");
            }
        }

        RouteValueDictionary routeValues = new RouteValueDictionary(htmlAttributes);
        if (routeValues != null)
        {
            foreach (var attribute in validationAttributes)
            {
                routeValues.Add(attribute.Key, attribute.Value);
            }
            return html.RadioButtonFor(expression, values, routeValues);
        }
        return html.RadioButtonFor(expression, values, validationAttributes);
    }

[Required]
    [Display(Name = "Delivery Method")]
    public int? DeliveryMethod { get; set; }

<input aria-describedby="deliverymethod-valMsg" aria-invalid="true"
    class="input-validation-error" data-val="true" data-val-number="The field Delivery Method must be a number."
    data-val-required="The Delivery Method field is required." id="DeliveryMethod_-1"
    name="DeliveryMethod" type="radio" value="-1">